Pediatric Hydrops Fetalis

Updated: Jul 25, 2017
Author: Ashraf H Hamdan, MD, MBBCh, MSc, MRCP, FAAP; Chief Editor: Dharmendra J Nimavat, MD, FAAP 



Hydrops fetalis (fetal hydrops) is a serious fetal condition defined as abnormal accumulation of fluid in two or more fetal compartments, including ascites, pleural effusion, pericardial effusion, and skin edema. In some patients, it may also be associated with polyhydramnios and placental edema. Hydrops is usually first recognized by ultrasonographic examination during the first or second trimester of gestation. Significant fluid collections are easily detected, but fluid accumulation may also be limited and thus escape routine ultrasonographic detection.

Hydrops fetalis has been a well-recognized fetal and neonatal condition throughout history. Until the latter half of the 20th century, it was believed to be due to Rhesus (Rh) blood group isoimmunization of the fetus. More recent recognition of factors other than isoimmune hemolytic disease that can cause or be associated with fetal hydrops led to the use of the term nonimmune hydrops to identify those cases in which the fetal disorder was caused by factors other than isoimmunization.

In the 1970s, the major cause of immune hydrops (ie, RhD antigen) was conquered with the use of immunoglobulin (Ig) prophylaxis in at-risk mothers. Before routine immunization of Rh-negative mothers, most cases of hydrops were due to erythroblastosis from Rh alloimmunization. With the introduction of widespread immunoprophylaxis for red blood cell alloimmunization and the use of in-utero transfusions for immune hydrops therapy, nonimmune causes have become responsible for at least 85% of all cases of fetal hydrops. Nevertheless, in developing countries, the incidence of immune fetal hydrops is still high.

For patient education resources, see the Heart Health Center, as well as Supraventricular Tachycardia (SVT, PSVT).


Several hypotheses regarding the pathophysiologic events that lead to fetal hydrops have been suggested. The basic mechanism for the formation of fetal hydrops is an imbalance of interstitial fluid production and the lymphatic return. Fluid accumulation in the fetus can result from congestive heart failure, obstructed lymphatic flow, or decreased plasma osmotic pressure. The fetus is particularly susceptible to interstitial fluid accumulation because of its greater capillary permeability, compliant interstitial compartments, and vulnerability to venous pressure on lymphatic return.

Compensatory mechanisms for maintaining homeostasis during hypoxia that results from underlying disease include increased efficiency of oxygen extraction; redistribution of blood flow to the brain, heart, and adrenals, thus causing renal tubular damage; volume augmentation to enhance cardiac output; and marked activation of the renin-angiotensin system. Unfortunately, these mechanisms also increase venous pressure and ultimately produce interstitial fluid accumulation and characteristic hydropic changes in the fetus. Increased venous pressure contributes to edema and effusion by increasing the capillary hydrostatic pressure and decreasing the lymphatic return. Impaired renal function causes oliguria or anuria and, subsequently, hydrops.[1]

Furthermore, the hepatic synthesis of albumin may be impaired owing to decreased hepatic perfusion and increased extramedullary hematopoiesis. Because albumin acts as the predominant oncotically active plasma protein, hypoalbuminemia increases transcapillary fluid movement at times of circulatory compromise.

Hydrops has been produced in the ovine fetus by anemia, tachyarrhythmia, occlusion of lymphatic drainage, and obstruction of cardiac venous return. Hypoproteinemia and hypoalbuminemia are common in human hydrops, and reduced intravascular oncotic pressure has been speculated to be a primary cause for the disorder. However, in the sheep model, a 41% reduction in total serum protein accompanied by a 44% decline in colloid osmotic pressure failed to produce fetal hydrops.[2] Furthermore, a study in humans showed that, despite a significant negative correlation between the fetal serum albumin level and the degree of fetal hydrops, most fetuses with hydrops had albumin levels within the reference range.[3] These results suggest that hypoalbuminemia is unlikely the sole cause for the primary onset of hydrops.

A closer look at the animal studies provides the clues necessary to understand the pathophysiology of hydrops. In one study, profound anemia was induced in fetal sheep; the hydrops that resulted was unrelated to hematocrit levels, blood gas levels, acid-base balance, plasma proteins, colloid oncotic pressure, or aortic pressure.[4]  The investigators found the difference was in the central venous pressure (CVP), which was much higher in persons with hydrops. The hematocrit level was reduced by 45% in a study of particular note; however, the CVP was maintained unchanged, and no fetus developed hydrops under these conditions.

Induced fetal tachyarrhythmia has led to fetal hydrops in several studies. Key to the development of fetal hydrops in these studies was an elevation in CVP; the anemia was only of indirect importance. The CVP was markedly elevated, with a range of 25-31 mm Hg in one study. In other reports, hydrops induced by sustained fetal tachycardia was unrelated to levels of blood gases, plasma protein, or albumin turnover; however, a 75-100% increase in CVP was observed in the fetuses that developed hydrops.

Excision of major lymphatic ducts produced fetal hydrops in sheep models. A related study demonstrated an exquisite, linear, inverse relationship between the lymphatic outflow pressure and the CVP; a rise in the CVP of 1 mm Hg reduced lymph flow 13%, and flow stopped at a CVP of 12 mm Hg.[5] These results were confirmed by other observations of linear decline in lymph flow when the CVP exceeds 5 mm Hg and a cessation of flow at CVPs greater than 18 mm Hg.

Also of note is a computer simulation model in which cardiovascular and fluid electrolyte disturbances (eg, severe anemia, lymphatic obstruction, excess fluid and electrolyte loads, elevation in angiotensin levels) and compensating homeostatic mechanisms have been examined. This model demonstrated that "...fetal cardiac failure constituted the strongest stimulus for the formation of fetal edema...",[6] thus further substantiating the pivotal role of CVP in the development of fetal hydrops.

Many other physiologic disturbances are associated with human fetal hydrops. Elevated levels of aldosterone, renin, norepinephrine, and angiotensin-I are likely to be secondary consequences. Although infusion of angiotensin-I led to fetal hydrops in nephrectomized sheep, the four-fold rise in the CVP was probably the primary cause of the hydrops. The meaning of increased levels of coenzyme Q10, placental vascular endothelial growth factor, and endothelin and decreased cytokine interleukin-3 levels is unclear at this time.

However, of particular interest is the three- to five-fold increase in atrial natriuretic peptide (ANP) that accompanies both human fetal hydrops (with cardiac anomaly or isoimmunization)[7, 8, 9, 10] and ovine hydrops (induced by obstruction of venous return, sustained tachycardia, or induced anemia).[11] A return of ANP levels to normal parallels the resolution of hydrops. These observations and the observations that vascular permeation of albumin is enhanced and cardiovascular and renal homeostatic adaptations are influenced by this peptide suggest an important role for ANP in fetal hydrops.

Evidence of low fetal plasma levels of cyclic guanosine monophosphate suggests that reduced nitric oxide production due to injury of fetal vascular endothelial cells may be involved in the development of fetal hydrops.[11] This isolated observation requires confirmation and further study.

Despite numerous case reports, decades of clinical experience, and several research studies regarding the etiology and pathogenesis of hydrops, many questions still remain. Currently, which fetal neural and hormonal mechanisms induce and maintain the redistribution of blood flow, and which mechanisms allow metabolic disorders to cause hydrops, are almost completely unknown.[1]


Hydrops fetalis is a nonspecific finding that is easily detected using prenatal ultrasonography. Despite extensive pre- and postnatal investigations, including postmortem pathologic examination of the fetus, the etiology may remain unknown in about 15-25% of cases of nonimmune hydrops fetalis.

Most patients with hydrops diagnosed in early fetal life have chromosomal anomalies, whereas cases diagnosed after the second trimester are caused mainly by cardiovascular diseases. In a study 156 cases of hydrops in a neonatal intensive care unit (NICU), Lin et al found the major etiology and associated diagnosis consisted of 35.9% of nonimmune anemia, 9.6% of cardiac abnormalities, 7.1% of intrauterine infection, 6.4% of twin problems, 5.8% of meconium peritonitis, 5.1% of thoracic-lung disease, 4.5% of chromosomal abnormalities, and 1.9% of immune anemia.[12] Alpha thalassemia was the most common nonimmune anemia (96%). An etiology and associated diagnosis could be determined in 81.4% of cases.[12]

Diagnostic categories

Hydrops is an end-stage process for numerous fetal diseases. One study reviewed 225 relevant nonimmune hydrops fetalis articles that described 6,361 individuals.[13, 14]  The investigators established 14 different diagnostic categories, with all 6,361 patients subclassified into one of the following:

  • Cardiovascular (21.7%)

  • Hematologic (10.4%)

  • Chromosomal (13.4%)

  • Syndromic (4.4%)

  • Lymphatic dysplasia (5.7%)

  • Inborn errors of metabolism (1.1%)

  • Infections (6.7%)

  • Thoracic (6%)

  • Urinary tract malformations (2.3%)

  • Extrathoracic tumors (0.7%)

  • Placental (5.6%)

  • Gastrointestinal (0.5%)

  • Miscellaneous (3.7%)

  • Idiopathic (17.8%)

Causes can be grouped in six broad categories: cardiovascular, genetic abnormalities, intrathoracic malformations, hematologic disorders, infectious conditions, and idiopathic forms.

Hematologic causes

Hematologic causes that lead to profound anemia and have been recognized to trigger hydrops fetalis are summarized below.

Isoimmunization (hemolytic disease of the newborn, erythroblastosis) includes the following:

  • Rh (most commonly D; also C, c, E, e)

  • Kell (K, k, Kp, Js[B])

  • ABO

  • MNSs (M, to date)

  • Duffy (Fyb)

Other hemolytic disorders include the following:

  • Glucose phosphate isomerase deficiency (autosomal recessive)

  • Pyruvate kinase deficiency (autosomal recessive)

  • Glucose-6-phosphate dehydrogenase (G-6-PD) deficiency (X-linked dominant)

Disorders of red blood cell (RBC) production include the following:

  • Congenital dyserythropoietic anemia types I and II (autosomal dominant)

  • Diamond-Blackfan syndrome (autosomal dominant)

  • Lethal hereditary spherocytosis (spectrin synthesis defects) (autosomal recessive)

  • Congenital erythropoietic porphyria (Günther disease) (autosomal recessive)

  • Leukemia (usually associated with Down or Noonan syndrome)

  • Alpha-thalassemia (Bart hemoglobinopathy)[15]

  • Parvovirus B19 (B19V)[16]

Fetal hemorrhage causes include the following:

  • Intracranial or intraventricular

  • Hepatic laceration or subcapsular

  • Placental subchorial

  • Tumors (especially sacrococcygeal teratoma)

  • Fetomaternal hemorrhage

  • Twin-to-twin transfusion

  • Isoimmune fetal thrombocytopenia

Rh disease was previouslyconsidered the usual cause of fetal hydrops. The use of RhoGAM in the at-risk mother, administered prior to maternal isoimmunization, should have made this an entirely preventable disorder. Sadly, this has not been the case. Although a dramatic reduction in RhD sensitization has been achieved with RhoGAM,[17] the disorder has stubbornly persisted in a small group of women, many of whom have become isoimmunized from repeated exposure to foreign RBC antigens on contaminated needles used for administering illicit drugs. One study noted this cause for one in five women with Rh sensitization; the prevalence of hydrops in this group was a stunning 80%.[18]  More recently, the rise in illicit intravenous (IV) opioid use during pregnancy has been reported to lead to isoimmune hemolysis in the fetus, which results in fetal death or severe hydrops fetalis.[19] Clinicians should be aware of this consequence; thus, careful history taking and screening is required.

The reduced prevalence of RhD disease has made fetal hemolytic anemias secondary to maternal isoimmunization with other Rh-group and other blood group antigens more apparent. Many of these result in profound fetal anemia and hydrops. Because many other such antigens are likely, maternal antibody screening should at least search for those already demonstrated to lead to fetal hydrops.

Molecular genetic technologies, specifically polymerase chain reaction (PCR) testing, have been particularly demonstrated to provide more precise and complete genotyping. Other heritable fetal hemolytic anemias have been associated with fetal hydrops. Most are uncommon, autosomal recessive genetic diseases (eg, pyruvate kinase deficiency, glucose phophate isomerase deficiency), and their association with fetal hydrops is limited to one or two reports. G-6-PD deficiency is a more common, X-linked recessive disorder; however, G-6-PD has been infrequently associated with fetal hydrops.

Making the diagnosis is important in these rare conditions, because they are compatible with a relatively normal life and fetal transfusions should be effective. Fetal RBC hemolysis from placental transfer of maternal immunoglobulin (Ig) G antibody against fetal RBC antigens (isoimmune disease) continues to account for approximately 15-20% of individuals with hydrops fetalis.

Early and precise diagnosis is of enormous importance, because highly effective fetal therapy is available and long-term outcome is unimpaired in infants with these causes for hydrops. Although fetal imaging confirms the presence of hydrops, it does so only after the fact. Thus, referral to a maternal-fetal medicine specialist is very beneficial. Studies preceding and predicting fetal deterioration include amniotic fluid bilirubin (delta optical density at 450 µ using Liley extrapolations), and measurement of fetal hematocrit and hemoglobin levels by direct sampling using cordocentesis. The degree of fetal anemia is indirectly measured by the middle cerebral artery velocity using Doppler ultrasonography.

Disorders of RBC production, resulting in functional fetal aplastic anemia, are particularly important causes of fetal hydrops. The role of infection with B19V is increasingly recognized. Use of a sensitive and precise diagnostic test (PCR) has demonstrated that perhaps 20% of fetal hydrops is associated with parvovirus infection. During seasons of particularly high prevalence, the proportion is much higher. Early diagnosis is crucial because fetal treatment by direct transfusion has been effective, the virus has no teratogenic effects, and growth and development of the survivors appear to be normal.

Heritable disorders of hemoglobin alpha-chain production are important causes of hydrops in Asian populations. These hemoglobinopathies have become increasingly relevant in the United States because of relatively recent immigration patterns, particularly in the West. A report from Hawaii over a 10-year period identified alpha-thalassemia as the single most important cause of fetal hydrops.[20]  Homozygous alpha-thalassemia, with deletion of all four alpha-globin genes, results in the total absence of alpha-hemoglobin chains in the fetus. This condition, ranging from 1 in 500 to 1 in 1500 in a Thai population, has been considered to be a fatal fetal condition (Bart hydrops).

A handful of survivors of hydrops fetalis due to alpha-thalassemia have been reported; however, all required fetal transfusions, all required repeated frequent transfusions after birth, and all surviving males had hypospadias.[21]  Thus, some healthcare professionals have questioned the practical and ethical basis of fetal and neonatal treatment. However, opportunities for treatment, such as stem cell transplantation, bone marrow transplantation, and gene replacement therapy, may hold promise for future infants with this condition. Fetal diagnosis of the condition has been confirmed (using PCR) from fetal DNA samples of chorionic villus, fetal fibroblast, and from fetal blood.

Once disorders of hemoglobin alpha-chain production are confirmed, fetal interventions have been based on hematocrit and hemoglobin levels obtained by direct cordocentesis. Ultrasonographic findings are nonspecific, and they occur late. Several simple maternal screening techniques have been suggested, but DNA-based studies using a testing system that allows unequivocal identification of haplotypes commonly detected in Asian Americans (-SEA in 62%, -alpha 3.7 in 27%, -FIL in 11%) appear to be most promising in this country.  Despite the generally gloomy outlook and uncertain treatment of the infant with fetal hydrops, early diagnosis of the condition is essential as maternal morbidity is very high with fetal hydrops due to alpha-thalassemia. A multiplex PCR assay developed by Jomoui et al appears to show promise in providing an accurate prenatal diagnosis of Bart hydrops fetalis syndrome.[15]

Other heritable disorders of RBC production are listed above, but none is very common. Some are fatal, but most are manageable after birth; some are associated with malformation syndromes. These heritable disorders all lead to hydrops in the same manner, as do the other conditions listed above.

Profound anemia leads to high-output cardiac failure and increased central venous pressure (CVP). Early and precise diagnosis is important for fetuses with correctable conditions (eg, need for and timing of fetal transfusions) and for fetuses with conditions that are not correctable (to permit parents to understand options and participate in decisions about pregnancy management). Gene therapy may also hold promise for some of these babies in the future.

Fetal hemorrhage is another important cause of fetal hydrops. Acute bleeding may be local or more generalized. Unless the origin is from a tumor mass, the bleeding may not be recognized early enough to intervene. Thus, fetal imaging is essential, and a careful examination, particularly of those sites where bleeding has been associated with hydrops, is essential for prompt and proper fetal treatment.

Isoimmune fetal thrombocytopenia is probably more common than has been reported and, because treatment may be effective in this condition, maternal screening for platelet antibodies should be routine in all cases in which the cause of fetal hydrops remains undetermined.

Sacrococcygeal teratoma is relatively common,[22, 23] accounting for a measurable proportion of incidents of fetal hydrops. Controlled trials are needed to be certain that currently proposed interventions are more helpful than harmful, but these interventions hold considerable promise. Effective treatment is especially important for this condition because associated anomalies are rare, and fully normal development is possible. Once again, fetal imaging studies are the cornerstone for diagnosis and management of sacrococcygeal teratoma.[24]

The fetus may bleed into the mother, and this hemorrhage may be severe enough to lead to fetal death or hydrops. Disruptions of the fetomaternal circulation may be placental or related to tumors (choriocarcinoma, chorangioma), trauma, or partial placental abruption.

Early diagnosis of fetomaternal hemorrhage requires a maternal blood smear to assess the proportion of circulating cells with fetal hemoglobin (resistant to acid elution). Unfortunately, automated modifications of this test are less specific and sensitive than the original Kleihauer-Betke test, and several newer tests have been proposed. Of these tests, the most promising appear to be either immunofluorescent flow cytometry or DNA analysis using PCR. It is difficult to determine which test to use and when to perform it because, in most reported cases, the diagnosis is usually too late to allow effective fetal intervention.

The earliest warning of the condition in most recent series has been reduced fetal body movements accompanied by sinusoidal fetal heart rate patterns and altered fetal biophysical profile. Confirmation of fetal anemia by direct cordocentesis is the final step to transfusion. Unfortunately, fetal transfusion has often been ineffective due to continued, repeated, massive fetal hemorrhages.

Placental vascular anastomoses are present in virtually all monochorionic monozygotic pregnancies. Twin-to-twin transfusion is balanced in most circumstances, with no excessive accumulation or loss for either twin. Sizable hemorrhages or unbalanced transfusion occurs in 5-30% of these pregnancies, leaving one twin anemic and the other polycythemic. This may lead to fetal death, impaired fetal growth, high-output cardiac failure from hypovolemic shock, congestive failure from volume overload, or hydrops fetalis, depending on the size of the bleed and whether it is acute or chronic. Extremely early twin-to-twin transfusion may result in fetal acardia; somewhat later, they may be detected as fetus papyraceous or as a stuck twin or vanishing twin.

Although some placental studies suggest fewer (rather than more) vascular anastomoses with resultant trapping of blood in the recipient fetus, other placental studies demonstrate excessive and abnormal placental vascular communications. Velamentous cord insertion is much more common in those fetuses with large shunts. Curiously, the recipient (polycythemic) twin usually develops hydrops, not the (anemic) donor. Even more interestingly, death of the hydropic twin (whether untreated and/or spontaneous, following fetal therapy, or after selective feticide) is not uncommonly followed by the development of hydrops in the remaining twin.

The reasons for all these events remain causes for speculation. Definitive diagnosis is also surprisingly difficult because hydrops may occur in either (or both) twin(s), disparities in fetal size may not be present, and fetal hemoglobin or hematocrit levels may be well outside the reference range (high or low) in the absence of any hydrops.

Ultrasonographic evidence of same-sex twins, a monochorionic placenta, with hydramnios in one sac and oligohydramnios in the other sac, is often used to make the diagnosis. These findings and disparities in fetal sizes (15%-25%) are useful, but unfortunately they are not definitive. Determination of fetal hemoglobins by cordocentesis is used; however, differences in fetal hemoglobin concentration exceeding 5 g/dL are common in the absence of hydrops and, conversely, differences less than this may be found in individuals with hydrops.

Significant differences in serum protein levels may also be observed in twins with hydrops fetalis, and atrial natriuretic factor (ANP) concentrations are usually high. Unfortunately, none of these findings are diagnostic. Clearly, earlier and more precise fetal diagnostic methods, which measure the degree of functional dysfunction, are needed.

Most promising in this regard are pulsed Doppler ultrasonographic measurements of umbilical vessel blood velocity. Such studies have the potential to provide an earlier window of opportunity for fetal diagnosis and treatment. The outcome is surprisingly poor in this condition. Most twins with hydrops die before birth (42%-86%), and a shocking proportion of survivors of the condition have cardiovascular and neurologic damage. Ultrasonographic studies demonstrate cerebral white matter damage, suggesting antenatal necrosis in approximately one third. Follow-up studies of neurodevelopment suggest serious impairment in approximately one quarter of surviving twins.

Many (if not most) surviving twins have significant cardiomyopathy (predominantly right-sided), usually associated with pulmonary outflow obstruction; pulmonary artery calcification and endocardial fibroelastosis are also common. Neutropenia, impaired fetal growth, reduced bone density, and mineralization have been observed in the surviving donors. Optic nerve hypoplasia has been reported, and peripheral vascular ischemic necrosis with gangrene of the distal extremities has been observed in several individuals with the condition. Coagulopathy and embolic phenomena were speculated in many early studies; however, scant evidence for them is present in more recent reports. Very premature delivery is common and undoubtedly contributes to the morbidity and mortality.

Treatment successes have been reported with transfusion of the anemic fetus, plasmapheresis of the polycythemic twin, laser ablation of placental vascular anastomoses, and amnioreduction; however, failures and serious complications have also been reported with each of these. See Twin-to-Twin Transfusion Syndrome.

Hydrops fetalis is the final common hemodynamic pathway for various fetal cardiovascular pathologies, including high-output states associated with fetal anemia or arteriovenous fistulas and abnormalities of both cardiac structure and rhythm. Cardiovascular problems that cause or are associated with hydrops are summarized below. Although extensive, the list is inevitably incomplete because new associations are reported each year.

Cardiac causes

Common cardiac causes include structural anomalies, dysrhythmias, tumors, as well as cardiomyopathy and myocarditis.[25]

Structural anomalies

Abnormalities of left ventricular outflow include the following:

  • Aortic valvular stenosis

  • Aortic valvular atresia

  • Coarctation of the aorta

  • Aortico-left ventricular tunnel

  • Atrioventricular canal

  • Left ventricular aneurysm

  • Truncus arteriosus

  • Hypoplastic left heart

  • Spongiosum heart

  • Endocardial fibroelastosis

Abnormalities of right ventricular outflow include the following:

  • Pulmonary valvular atresia or insufficiency

  • Ebstein anomaly

Other vascular malformations include the following:

  • Arteriovenous malformations (AVMs)

  • Diffuse hemangiomatosis

  • Placental hemangioma

  • Umbilical cord hemangioma

  • Hepatic hemangioendothelioma

  • Abdominal hemangioma

  • Pulmonary arteriovenous fistula

  • Cervical hemangioendothelioma

  • Paratracheal hemangioma

  • Cutaneous cavernous hemangioma

  • AVMs of the brain

Nonstructural anomalies

Obstruction of venous return includes the following:

  • Superior or inferior vena cava occlusion

  • Absent ductus venosus

  • Umbilical cord torsion or varix

  • Intrathoracic or abdominal tumors or masses

  • Disorders of lymphatic drainage

Other cardiac nonstructural anomalies include the following:

  • Supraventricular tachycardia

  • Congenital heart block

  • Prenatal closure of the foramen ovale or ductus arteriosus

  • Myocarditis

  • Idiopathic arterial calcification or hypercalcemia

  • Intrapericardial teratoma

Cardiovascular diseases are one of the main causes for nonimmune hydrops fetalis. Congenital structural anomalies of the heart may be present in as many as one in four infants with hydrops; both right-heart and left-heart anomalies, systolic-overload and diastolic-overload conditions, high-output conditions, and congestive situations are represented. Although many cardiac malformations have been reported, the most common were atrioventricular (AV) septal defects.

Structural cardiac defects are commonly accompanied by other anomalies and are often associated with cytogenic abnormalities. Examples include the association between coarctation of the aorta and Turner syndrome, the relationship between the AV canal and/or endocardial cushion defects and Down syndrome, and the common association of Turner syndrome with cystic hygroma, left-sided lymphatic flow defects, and left-heart outflow defects.

Fibroelastosis may be an isolated abnormality; however, fibroelastosis more commonly represents an endocardial response to chronic fetal myocardial stress. Prenatal detection of a cardiac defect should always trigger a careful search for other malformations, and karyotyping should be performed in all such fetuses. AVMs are the often cited causes of hydrops; they are listed individually above.

Impaired right-heart filling is also an important cause of hydrops. Although uncommon, umbilical or vena caval thromboses have been noted. Theoretically, they may be correctable if diagnosed early enough. Conversely, tumor compression is a frequently reported cause of hydrops. Several of these masses involve lymphatic malformation and/or obstruction; cystic hygroma is a particularly notable example.

Prenatal closure of the foramen ovale or ductus arteriosus prematurely converts the (parallel) fetal circulation to a (serial) postnatal circulation; the associated problems are obvious. Most recorded instances of premature ductal closure are iatrogenic, related to maternal administration of indomethacin or sodium diclofenac.

Several instances of idiopathic arterial calcification with hydrops have been reported. In one such incident, fetal serum calcium levels were elevated, and a possible association with Williams syndrome was suggested. In three other cases, lysosomal storage diseases were present (Gaucher, sialidosis, galactosialidosis). No associations were noted in four cases. Hydropic recipients of twin-to-twin transfusion who survive also usually have pulmonary artery calcification.

Fetal supraventricular tachycardias are important causes of hydrops because they can be diagnosed accurately by cardiac imaging in early pregnancy, they may be treated effectively before hydrops develops and, because associated malformations or syndromes are rare, they have anticipated good outcomes. Whether an AV block is present (atrial flutter) or not (tachyarrhythmia), survival rates of 85%-95% are typical, and neurodevelopmental outcome is usually normal. Males are affected more than in females (2:1). Clinical experience and animal model studies indicate that hydrops can occur with sustained cardiac rates of less than 220-230 beats per minute (bpm) and that the risk is related directly to the degree of prematurity.

Congenital heart block is also often associated with hydrops. The diagnosis is made using cardiac imaging or with an electrocardiogram (ECG) in the newborn; rates are always less than 90 bpm and usually below 65 bpm. Approximately two thirds to three fourths occur in pregnancies complicated by maternal collagen disease. Maternal immunoglobulin (Ig) G antinuclear antibodies cross the placenta and attack fetal collagen in the conduction bundle. Why some fetuses develop congenital heart block and others do not is unclear; however, an association with human leukocyte antigen (HLA) types (HLA-DR3, among others) has been suggested.

Treatment with various drugs has generally been unsuccessful, as has fetal surgery for pacing. Evidence exists to suggest corticosteroid therapy may be of benefit.

Virtually all of the remaining babies, whose mothers have no collagen disorder, have serious, complicated, cardiac structural defects. The most common lesions are AV canal and/or endocardial cushion defects, transposition of the great vessels, and other isomerisms. The outcomes for these babies are grim. Mortality is 25%-35% if the cardiac structure is normal; however, many survivors require neonatal surgery for pacing, and sparse information is available on long-term outlook. Because the cardiac structural abnormalities are so serious and complex, mortality and morbidity are much higher if cardiac anomalies are present.

Infectious causes

The immature fetus is particularly susceptible to overwhelming viral and bacterial infection. Those pathogens that do not kill quickly may cause smoldering generalized infections with myocarditis, suppressed erythropoiesis and myelopoiesis, hemolysis, and hepatitis. Such infections may lead to hydrops fetalis. Several causative pathogens reported to date are listed below. Among the infectious etiologies, the most common causes are cytomegalovirus (CMV), toxoplasmosis, syphilis, and B19V infection.

Infectious causes of hydrops fetalis are as follows:

  • B19V

  • CMV

  • Syphilis

  • Herpes simplex[26]

  • Toxoplasmosis

  • Hepatitis B

  • Adenovirus

  • Ureaplasma urealyticum

  • Coxsackievirus type B

  • Listeria monocytogenes

  • Enterovirus[27]

  • Lymphocytic choriomeningitis virus (LCMV)[28]

The association of congenital syphilis with hydrops is classic. Fetal and placental edema accompanied by serous effusions first was described generations ago. However, the surprising frequency with which maternal serologic tests for syphilis may appear negative in this condition is less well known.

The prozone phenomenon, observed during primary and secondary maternal syphilis, occurs when a higher-than-optimal amount of anti-syphilis antibody in the tested maternal sera prevents the flocculation reaction typifying a positive result in reagin tests. In these circumstances, dilution of the tested serum is necessary to make the correct diagnosis. Thus, serum dilution (to as much as 1:1024 or greater) should be routine in high-risk situations and should certainly be used in any individual in whom fetal hydrops of unknown etiology is present.

Early, accurate diagnosis of this infection is critical because fetal treatment is available and effective. Several viral infections have been associated with fetal hydrops. The number of viruses implicated and the frequency of these cases have paralleled the increased recognition of this association and the improved simplicity and sensitivity of diagnostic methods. Hydrops in these conditions appears to be the cumulative result of viral effects on marrow, myocardium, and vascular endothelium. Currently, reports of effective fetal treatment are rare.

Human parvovirus B19 is a single-stranded DNA virus that usually infects rapidly dividing cell lines, such as erythroid progenitor cells. An estimated 1%-5% of pregnant women are infected with parvovirus B19.[16]  This virus has been shown to cause a congenital infection syndrome, manifested by rash, anemia, hepatomegaly, and cardiomegaly, and infection can lead to miscarriage or nonimmune hydrops fetalis.[16] Because most pregnant women who become infected with B19V are asymptomatic, determining the risk of fetal infection, fetal wastage, and nonimmune hydrops fetalis is difficult.

In infected pregnant women, B19V is believed to affect the fetus approximately 30% of the time; however, only 2%-10% of infected fetuses experience poor outcomes. Some evidence has demonstrated that acute B19V infection is a common cause of fetal hydrops.[29]  The virus was first identified in 1974 and was first linked with fetal hydrops 10 years later. Evidence published since then suggests this virus may be the single most important currently recognized cause of fetal hydrops. Parvovirus may be the cause of as many as one third of all incidents of hydrops fetalis.

The outcome following B19V infection is surprisingly good; spontaneous resolution occurs in approximately one third of such incidents, and approximately 85% of those who receive fetal transfusions survive. The virus is not teratogenic and, despite reports of viral persistence in myocardial and brain tissues, neurodevelopmental outcome in survivors appears to be normal. Early, accurate diagnosis, using maternal serologic and/or molecular biologic PCR techniques, is essential. Positive results are usually confirmed by direct fetal PCR, hemoglobin, hematocrit, and platelet studies to determine a proper treatment plan.

An interesting association between hydrops and fetal meconium peritonitis is also recognized. At least 16 such cases are found in the literature. No baby reported before 1991 had evidence of infection; however, CMV (1), hepatitis B (1), and B19V (5) were found in 7 of 8 cases reported since 1991. The only instance of meconium peritonitis and hydrops without confirmed infection in these later reports was likely iatrogenic, because it followed paracentesis with subsequent placement of a peritoneoamniotic shunt. These observations suggest that the coexistence of hydrops and meconium peritonitis should be assumed to be related to fetal infection until proven otherwise.

LCMV is a member of the Arenavirus family that mainly infects small rodents. Humans may become infected by inhalation of the virus particles when in contact with infected rodent urine. In immunocompetent humans, LCMV infection is mostly asymptomatic but it may cause mild febrile illness with aseptic meningitis, which is rarely fatal.

The incidence of LCMV infection during pregnancy is unknown but several cases of congenital infection have been reported. The main features of congenital LCMV infection include chorioretinitis, hydrocephaly or microcephaly, periventricular calcifications, and seizures. Fetal infection may result in fetal or neonatal death, and neurologic sequelae affect 84% of the surviving infants.

One report suggested that LCMV should be added to the list of causative agents of nonimmune hydrops fetalis.[28]  These viruses should be screened for in cases of unexplained fetal hydrops, especially when there is a possibility of maternal contacts with rodents and postmortem findings are suggestive of fetal infection.

Hydrops fetalis has been associated with more than 75 inborn errors of metabolism, chromosomal aberrations, and genetic syndromes. Approximately 50 of the more common errors are listed below. An additional 20 or more reports of imprecisely defined chromosomal or genetic syndromes identify hydrops as an incidental finding.

Metabolic disorders, genetic syndromes, and chromosomal abnormalities

Inborn errors of metabolism include the following:

  • Glycogen-storage disease, type IV

  • Lysosomal storage disease

    • Gaucher disease, type II (glucocerebroside deficiency)

    • Morquio disease (mucopolysaccharidosis, type IV-A)

    • Hurler syndrome (mucopolysaccharidosis, type 1H; alpha1-iduronidase deficiency)

    • Sly syndrome (mucopolysaccharidosis, type VII; beta-glucuronidase deficiency

    • Farber disease (disseminated lipogranulomatosis)

    • GM1 gangliosidosis, type I (beta-galactosidase deficiency)

    • Mucolipidosis I

    • I-cell disease (mucolipidosis II)

    • Niemann-Pick disease, type C

  • Salla disease (infantile sialic acid storage disorder [ISSD] or sialic acid storage disease, neuroaminidase deficiency)

  • Hypothyroidism and hyperthyroidism

  • Carnitine deficiency

Genetic syndromes (autosomal recessive, unless otherwise noted) include the following:

  • Achondrogenesis: type IB (Parenti-Fraccaro syndrome), type II (Langer-Saldino syndrome)

  • Arthrogryposis multiplex congenita: Toriello-Bauserman type, with congenital muscular dystrophy

  • Beemer-Langer (familial short-rib syndrome)

  • Blomstrand chondrodysplasia

  • Caffey disease (infantile cortical hyperostosis; uncertain inheritance)

  • Coffin-Lowry syndrome (X-linked dominant)

  • Cumming syndrome

  • Eagle-Barrett syndrome (prune-belly syndrome; 97% are male, thus probably X-linked)

  • Familial perinatal hemochromatosis

  • Fraser syndrome

  • Fryns syndrome

  • Greenberg dysplasia

  • Lethal congenital contracture syndrome

  • Lethal multiple pterygium syndrome (excess of males, thus probably X-linked)

  • Lethal short-limbed dwarfism

  • McKusick-Kaufman syndrome

  • Myotonic dystrophy (autosomal dominant)

  • Nemaline myopathy with fetal akinesia sequence

  • Noonan syndrome (autosomal dominant with variable penetrance)

  • Perlman/familial nephroblastomatosis syndrome (inheritance uncertain)

  • Simpson-Golabi-Behmel syndrome (X-linked [Xp22 or Xp26])

  • Sjögren syndrome A (uncertain inheritance)

  • Smith-Lemli-Opitz syndrome

  • Tuberous sclerosis (autosomal dominant)

  • Yellow nail dystrophy with lymphedema syndrome (autosomal dominant

Chromosomal syndromes include the following:

  • Beckwith-Wiedemann syndrome (trisomy 11p15)

  • Cri-du-chat syndrome (chromosomes 4 and 5)

  • Dehydrated hereditary stomatocytosis (16q23-qter)

  • Opitz G syndrome (5p duplication)

  • Pallister-Killian syndrome (isochrome 12p mosaicism)

  • Trisomies 10 (mosaic), 13, 15, 18, 21 (Down syndrome)

  • Turner syndrome (45, X)

The heterogeneity of this collection of associations is bewildering at first glance. However, the common thread that runs through them is useful for understanding: Most of the infants with hydrops associated with the conditions listed above have severe complex cardiac defects, disorders of lymphatic drainage, AVMs, impaired production of properly functioning RBCs, and/or thoracoabdominal masses that impair venous return to the heart. Thus, the same disturbed pathophysiology identified as causing hydrops in the animal studies is reflected in these conditions.

Inheritance for most of these conditions (when known) is autosomal, most often recessive. Because a few of these conditions are X-linked recessive, slightly more males are affected among this particular set of causes. Gene therapy may hold therapeutic promise for the future; however, outcomes are generally grim for babies with hydrops related to these etiologies. Accurate diagnosis is particularly important in affected infants despite their poor prognosis, because parental counseling is critical in the management of current and future pregnancies for these families.

Fetal hydrops has been associated with approximately 10 of the approximately 50 lysosomal storage disorders. Little doubt appears to exist that hydrops will be linked with most such inborn errors of metabolism in the near future.

Cystic hygroma are commonly associated with complex profound aberrations of lymphatic drainage. These lesions are usually found in the neck but may also be present in the abdomen or thoracic cavity. The incidence of cystic hygroma has been reported to be as high as 1 in 6,000 at birth and as high as 1 in 750 among spontaneously aborted fetuses.

Although some authors have reported cases of live birth after spontaneous resolution of the cystic lesion, the prognosis remains poor if the hygroma is associated with hydrops fetalis irrespective of karyotype. Two thirds to three fourths of fetuses with this tumor have chromosomal abnormalities (most commonly 45,XO), and those fetuses with normal chromosomes often have major malformations. The associations with Turner, Noonan, and lethal multiple pterygium syndromes are particularly notable.

Mortality is extremely high (85%-96%), but early precise diagnosis is important for the purposes of genetic counseling and pregnancy management. One report detailed a case of a fetus in which fetal cystic hygroma and hydrops fetalis spontaneously resolved, with subsequent delivery at 37 weeks' gestation of a living female infant with Noonan syndrome.[30]

Thoracic and abdominal tumors are common causes of fetal hydrops. This association makes physiologic sense because the location and size of these masses are likely to obstruct the return of venous or lymphatic fluids to the heart. Some tumors are commonly associated with major malformations and/or chromosomal abnormalities and, consequently, have a poor long-term prognosis. For example, upper airway obstructions are associated with other major malformations in more than half of the cases reported, and the association of fetal rhabdomyomas with tuberous sclerosis and complex cardiac malformations is well recognized.

Tumoral/mass causes

Intrathoracic tumors or masses include the following:

  • Pericardial teratoma

  • Rhabdomyoma

  • Mediastinal teratoma

  • Cervical vascular hamartoma

  • Pulmonary fibrosarcoma

  • Leiomyosarcoma

  • Pulmonary mesenchymal malformation

  • Lymphangiectasia

  • Bronchopulmonary sequestration

  • Congenital pulmonary airway malformation (CPAM)

  • Cystic adenomatoid malformation of the lung

  • Upper airway atresia or obstruction (laryngeal or tracheal)

  • Diaphragmatic hernia

  • Eventration of the diaphragm[31]

Abdominal tumors or masses include the following:

  • Metabolic nephroma

  • Polycystic kidneys

  • Neuroblastoma

  • Hepatic mesenchymal hamartoma

  • Hepatoblastoma

  • Ovarian cyst

Other conditions include the following:

  • Placental choriocarcinoma

  • Placental chorangioma

  • Cystic hygroma

  • Intussusception

  • Meconium peritonitis

  • Intracranial teratoma

  • Sacrococcygeal teratoma

Venous return is directly impaired by such conditions as pericardial teratomas and cardiac rhabdomyosarcomas. Upper airway (laryngeal, tracheal) atresia or obstruction leads to massive pulmonary overdistention and, thus, to impaired cardiac filling. Cystic hygromas are mentioned again because they comprise an important and common example of mass compression with obstruction of venous-lymphatic return. Meconium peritonitis is noted in tumor or mass causes and in the discussion of infectious causes. This redundancy is due to the fact that some observers have postulated an association with hydrops on the basis of mass effects on venous return; as noted earlier, the association is almost certainly one with fetal infection and consequent RBC aplasia.

Some of these conditions may lead to fetal hydrops not because of mass compression effects but because their intense vascularization may lead to arteriovenous shunting and/or to massive fetal hemorrhage. Such consequences are especially common with sacrococcygeal teratomas and with placental chorioangiomas. In both instances, fetal high-output cardiac failure may ultimately lead to fetal hydrops and/or death. Sacrococcygeal teratoma is associated with hydrops in one fifth to one third of cases in several case series; fetal coagulopathy, most commonly thrombocytopenia, is found in approximately the same proportion of cases. Tumor size as assessed using ultrasonography has not been demonstrated to be an independent prognostic factor; however, solid, highly vascular tumors lead to hydrops more often than those with a more cystic, less vascular structure.

Because chromosomal abnormalities and life-threatening anomalies are rare with sacrococcygeal sequestration, early diagnosis and aggressive fetal treatment are particularly important with this condition. Although bloody amniotic fluid secondary to the rupture of the highly vascular teratoma is not uncommon, the diagnosis in most cases has been made only after hydrops has developed.

Early routine fetal imaging may be the only way in which early diagnosis can be made in this condition; however, the low incidence of sacrococcygeal teratoma may preclude cost-effective screening for this condition. Elevated concentrations of alpha-fetoprotein (AFP) and/or acetylcholinesterase in the amniotic fluid have been found to accompany fetal sacrococcygeal teratoma, but the invasive sampling and low specificity appears to preclude these tests as routine screening procedures. Although placental chorioangiomas are common (present in approximately 1% of pregnancies), large vascular tumors with cardiovascular and hematologic consequences are very uncommon. When present, the pathophysiology of placental chorioangiomas is remarkably similar to that found with fetal sacrococcygeal teratomas. The diagnosis and techniques for early intervention are also similar.

Bronchopulmonary sequestration is a condition in which abnormal vascular supply and misplacement of a portion of the lung may lead to torsion of the affected lobes, profound obstruction of lymphatic and venous return, and tension hydrothorax. This sequence of events leads to fetal hydrops in perhaps one third of such cases. Although drainage of the hydrothorax, definitive diagnosis using color Doppler imaging, and fetal angiography have been described, and although fetal surgical excision of the affected portion of the lung may improve survival in this condition, nearly two thirds of these cases fail to be diagnosed before fetal death or birth occurs.

Congenital pulmonary airway malformation (CPAM), previously known as congenital cystic adenomatoid malformation (CAM), is a rare abnormality of lung development in which there is a hamartomatous overgrowth of the terminal bronchioles with subsequent suppression and lack of differentiation of the alveoli. CPAM of the lung may also lead to hydrops by mass compression of venous return.

Because CPAM is seldom associated with other malformations or with chromosomal abnormalities, and because fetal surgical maneuvers have demonstrated considerable promise with some forms of the disorder, early and precise diagnosis using fetal imaging techniques is critical. CPAM is a rare fetal lung disease with an excellent prognosis in the absence of fetal hydrops. CPAM associated with fetal hydrops carries a grave prognosis, but survival rates of 70% can be achieved by thoracoamniotic drainage in those with macrocystic lesions. Lee at al reported successful treatment of hydrops associated with CPAM using fetal percutaneous sclerotherapy by ethanolamine injection into the tumor and concluded that fetal percutaneous sclerotherapy can be used as a minimally invasive palliative strategy to treat CPAM-induced hydrops fetalis.[32]

Pulmonary capillary-alveolar development is abnormal in this condition, and three degrees of severity, described initially by Stocker, have been used to predict prognosis, as follows[33] :

  • Type I: Fetuses with large (>2 mm), isolated cysts seldom develop hydrops, and spontaneous remissions have been reported. Drainage or excision of individual cysts has also been reported with generally favorable outcomes.

  • Type II: Poorer prognosis is associated in fetuses with smaller (<2 mm) diffuse macrocysts, and isolated fetal pulmonary excisions have been proposed in those who develop hydrops.

  • Type III: In fetuses with microcystic disease, the affected lung appears solid, hydrops is common, and the outcome is generally unfavorable.

Compression of fetal lung, common with many of the tumor and mass etiologies, not only impairs cardiac return but also has an additional particularly serious consequence. External compression of developing fetal lung is known to impair both anatomic and biochemical maturation. Pulmonary hypoplasia, with a profound reduction in the number of functional alveolar units, is a common finding when fetal hydrops accompanies these conditions. Delayed or impaired maturation of pulmonary surfactant production is another consequence of impaired expansion of the fetal lung, thus worsening the already serious compromise of extreme prematurity in these babies.


United States data

The precise incidence of hydrops fetalis is difficult to elucidate, because many cases are not detected prior to intrauterine fetal death and some cases may resolve spontaneously in utero. The best estimate for how common this condition is in the United States is approximately 1 in 600 to 1 in 4,000 pregnancies. The incidence of immune hydrops has significantly decreased with the wide use of passive immunization using Rh immunoglobulin for Rh-negative mothers at 28 weeks' gestation (following suspected fetomaternal hemorrhage) and postpartum (following the delivery of an Rh-positive infant). The efficacy of this program has been demonstrated by a decline in the incidence of Rh hemolytic disease of the fetus or newborn, from 65 in 10,000 births in the United States in 1960 to 10.6 in 10,000 births in 1990.

More recently, data from the California Office of Statewide Health Planning and Development (2005-2012) reported in 2017 showed an incidence of 2.5 per 10,000 live-born infants with nonimmune hydrops fetalis.[34]  

International data

Hydrops fetalis is much more common in Southeast Asia. The best figures come from Thailand, where the expected frequency of hydrops, from homozygous alpha-thalassemia or Bart hydrops alone, is 1 in 500 to 1 in 1,500 pregnancies.[35]  A 2017 report of the genetic origin of α0-thalassemia (SEA deletion [-SEA]) in Southeast Asian populations found that 94.0% of Thai, 100% of Laotian, and 100% of Cambodian α0-thalassemia alleles were linked to haplotype H4 (AAGC), with a G allele (rs3760053) having a strong linkage disequilibrium with the α0-thalassemia allele.[15]

A retrospective review (2006-2013) of all 30 cases of fetal hydrops at a Singapore tertiary care hospital revealed 17 cases of Bart hydrops (all terminated in utero), 11 cases of nonimmune hydrops, and 2 cases of immune hydrops.[36]  In a separate retrospective review (2007-2014) of 482 cases of nonimmune hydrops fetalis in Southern China, the most common etiologies were Bart hydrops (61.8%), chormosomal abnomalities (13.5%), idiopathic (13.1%), and cardiac anomalies (6.4%).[37]

Accurate figures from the Mediterranean region are not available; however, the commonness of glucose-6-phosphate dehydrogenase (G-6-PD) deficiency and of defects in alpha-chain hemoglobin production in several populations from this region lead to the suspicion that the incidence of hydrops in that region is much higher than it is in the United States.

Race-related demographics

Ethnic influences are related almost entirely to cause. Selected examples include the importance of genetic variations in the alpha-chain structure of hemoglobin in Asian and Mediterranean populations in addition to the more serious nature of the hemolytic disease in black fetuses affected by maternal ABO-factor isoimmunization.

Sex-related demographics

Sex influences in incidence or outcome of hydrops fetalis are largely related to the cause of the condition. A significant proportion of fetal hydrops is caused by or associated with chromosomal abnormalities or syndromes. Many of these are X-linked disorders.

Because most individuals with hydrops fetalis are delivered quite prematurely, and because fetal pulmonary maturation takes place earlier in female than in male fetuses, male preterm infants are at greater risk for the pulmonary complications of a very preterm delivery. They are also at greater risk for infections (nosocomial or otherwise), which are quite common in very preterm infants. A striking example of the greater male risk is the nearly 13-fold increase in the odds ratio for development of hydrops in the male fetus with RhD hemolytic disease. Although a single precise risk figure is not available for the heterogeneous collection of cases that comprise hydrops fetalis, male fetuses appear to have a greater risk for occurrence, morbidity, and mortality.


Fetal hydrops carries a poor prognosis, especially in preterm infants, remains a complex condition with high mortality and morbidity.[38]  The prognosis partly depends on the underlying disease. The growing number of recognized etiologies requires a comprehensive and systematic search for causes, in particular for treatable or recurrent conditions.[39]  Several diseases can be treated in utero with potential good results; with aggressive postnatal care, the survival rate is increased in selected cases.

The outcome of hydrops fetalis also depends on gestational age at birth and serum albumin level. One study suggested that hydrops resulting from lymphatic malformations has a favorable outcome.[40]  Preterm birth at less than 34 weeks' gestation and a serum albumin concentration level of less than 2 g/dL are poor prognostic factors for survival. A strong association has been reported between gestational age, the presence of two or more serous cavity effusions, and poor outcome in infants with hydrops fetalis.[41]  More recently, investigators revealed that signficant factors for postnatal death in fetal hydrops infants with pleural effusion are gestational birth week and standard deviation score of birth weight.[38]

Outcomes in fetuses with antenatally diagnosed idiopathic nonimmune hydrops fetalis are similarly dependent on the underlying etiology, with the presence of ascites a prognostic factor for perinatal mortality.[42]  Unfortunately, fetal intervention in patients with nonimmune hydrops fetalis does not appear to offer a survival advantage.


The diagnosis and management of fetal hydrops have improved with advances in prenatal diagnostic and therapeutic interventions in conjunction with the advances in neonatal intensive care. However, fetal hydrops is still associated with a high mortality rate.

Estimates of mortality vary widely, from nearly zero to virtually 100%. Most case series report a 60%-90% mortality, although some improvements are notable in more recent reports. Many reasons for these variations are recognized, not least of which include the sophistication of diagnostic methods used and the complexity and costs of treatment.

However, the most important single factor is the cause of the hydrops. A significant proportion of these cases are caused or accompanied by multiple and complex congenital malformations of genetic and/or chromosomal origin, which by themselves are fatal at an early age. Many other causes are accompanied by masses or fluid accumulations, which compress the developing fetal lung and preclude its normal development. Thus, the presence or absence and potential prevention of pulmonary hypoplasia are of crucial importance.

One study showed that mortality rate was highest among neonates with congenital anomalies (57.7%) and lowest among neonates with congenital chylothorax (5.9%).[43]  Infants who died were more likely to be more premature, were sicker after birth, with lower 5-minute Apgar scores, and needed higher levels of support during the first day after birth.

Another highly important factor is the very premature delivery of most babies with hydrops consequent to conditions that distend the uterus and provoke early labor, or to therapeutic interventions (eg, fetal thoracentesis, paracentesis, complex fetal surgical procedures).

A 2017 report of data from the California Office of Statewide Health Planning and Development (2005-2012) regarding 1037 live-born infants with nonimmune hydrops fetalis revealed a 35.1% neonatal mortality and a 43.2% overall mortality at age 1 year.[34]  Poor prognostic factors were prematurity, polyhydramnios, and large for gestational age.

In a separate 2017 report that analyzed data from an international registry of 69 survivors with hemoglobin Bart hydrops fetalis, investigators found that more than half survived beyond age 5 years (n = 39; 56.5%), of whom half (n = 18; 26.1%) were older than 10 years.[44] Although intrauterine therapy appeared to be beneficial during the perinatal and neonatal periods, the investigators suggested that further benefits might not extend to long-term growth and neurodevelopment outcomes. Indeed, over time, about 40% of these patients had severe weight retardation and 50% had height retardation, and 20% had a neurodevelopment delay of 6 months or longer.[44]




A history suggesting the presence of any of the factors listed below should trigger an extensive diagnostic study for hydrops fetalis.

Maternal history

The following maternal factors warrant an investigation for hydrops fetalis:

  • Rh negative (d;d) blood type

  • Known presence of isoimmune blood group antibodies

  • Prior administration of blood products

  • Risks of illicit drug use

  • Collagen vascular disease

  • Thyroid disease or diabetes

  • Organ transplant (liver, kidney)

  • Blunt abdominal trauma (abuse, auto accident)

  • Coagulopathy

  • Use of indomethacin, sodium diclofenac, or potentially teratogenic drugs during pregnancy

  • Younger (35 years) maternal age

  • Risk factors for sexually transmitted diseases

  • Hemoglobinopathy (especially with Asian or Mediterranean ethnicity)

  • Occupational exposure to infants or young children

  • Pet cat

  • Current or recent community epidemic of viral illness

Family history

The following family history factors warrant an investigation for hydrops fetalis:

  • Prolonged or excessive jaundice in siblings as newborns

  • Presence of jaundice in other family members

  • Family history of twinning (specifically, monozygotic)

  • Family history of genetic disorders, chromosomal abnormalities, or metabolic diseases

  • Congenital malformation in previous child

  • Previous fetal death

  • Polyhydramnios or oligohydramnios in earlier pregnancies

  • Prior hydrops fetalis

  • Previous fetomaternal transfusion

  • Congenital heart disease in previous child

Physical Examination

The presence of any of the following maternal or fetal physical examination findings should prompt further diagnostic evaluation:

  • Twinning

  • Polyhydramnios or oligohydramnios

  • Exanthem or other evidence of intercurrent viral illness

  • Herpetic lesion or chancre

  • Decrease in fetal movements

  • Fetal tachyarrythmias



Diagnostic Considerations

Important considerations

Unique medicolegal issues primarily concern the difficult access to the fetus.

The keystone of management of hydrops fetalis is developing parental knowledge and understanding of all choices to obtain truly informed consent. Because the fetal condition is always urgent and time is short, development of this parental knowledge and understanding may represent a considerable challenge.

Medications given to the mother place her at risk; however, the same medications may ultimately reach the fetus in concentrations too low to be effective. In addition, a standard therapy has yet to be established.

The option of direct fetal access for drug administration has often been used; however, the invasive methods used inevitably place both mother and fetus at increased risk.

Similarly, direct fetal surgical maneuvers carry more risk for the fetus than similar procedures performed after birth; direct fetal surgical maneuvers also place the mother at increased risk.

Finally, inadvertent harm to the fetus places the clinician at medicolegal risk for a considerably longer period than is usual.

Special considerations

Mirror syndrome is a rare entity characterized by maternal disease that mimics fetal hydrops.[45] In mirror syndrome, maternal hypertension, edema, and often proteinuria are present in association with fetal hydrops.

Mirror syndrome is reported with various conditions associated with hydrops fetalis and is life threatening to both the mother and fetus if unnoticed and untreated. Prompt delivery is the treatment of choice.

The causal link between mirror syndrome and hydrops fetalis remains elusive.

Other problems to be considered

Consider the following in the evaluation of patients with suspected hydrops fetalis:

  • Hypoxic-ischemic brain injury in the newborn

  • Laryngeal stenosis

  • Pulmonary hypertension

  • Congenital heart disease

  • Prune-belly syndrome

  • Uncommon coagulopathies

Differential Diagnoses



Laboratory Studies

Timely referral to a maternal–fetal medicine specialist allows for detailed and comprehensive ultrasonographic examination and the early identification of any treatable causes of fetal hydrops.

Antenatal identification of the etiology would allow for appropriate counselling of parents and help clinicians provide parents with early options such as medical termination of pregnancy, planned delivery, or active antenatal treatment.

Diagnostic studies may be considered best by temporal grouping (fetal, maternal, placental, neonatal, postmortem). Assessments generally proceed from low-risk noninvasive tests to higher-risk invasive techniques as required for precise and complete diagnosis to properly manage the individual pregnancy.

Obtain several maternal laboratory studies concurrent with the initial fetal imaging assessment.

Assessment of maternal blood type (red blood cells [RBCs]) and antibody screen (identification, and quantitation when indicated, of maternal plasma antibodies) are standard screening tests recommended in most guidelines for prenatal care. The introduction of newer molecular genetic techniques (eg, polymerase chain reaction [PCR]) has demonstrated considerable promise; however, definitive comparisons with standard methods are not yet available. More than 85% of Rh-sensitized women whose anti-D titers were 1:512 or higher were found to have human leukocyte antigen (HLA) type DQBI allele*0201. Although this single study suggests that HLA typing may be of value in the prospective management of isoimmunization, such an observation requires confirmation and further study.

Qualitative and quantitative estimates of the proportion of RBCs containing fetal hemoglobin in the maternal circulation are of particular value, including the following:

  • The Kleihauer-Betke technique depends on the difference in vulnerability of cells containing fetal hemoglobin from those with adult hemoglobin when subjected to acid-elution.

  • A newer method using flow cytometry has also been found to be useful.

  • Results using either method must be interpreted with considerable caution, because poor sensitivity and specificity of these diagnostic tests has been demonstrated in several studies.

The search for maternal-fetal infection must be intensive.

Syphilis serology was a standard prenatal screening test for decades. More recently, the test has been used more selectively, despite the absence of any good evidence for this change. If fetal hydrops is suspected, syphilis serology is mandatory, with repeat serial testing and, very importantly, with dilution of maternal serum. The prozone effect has been demonstrated repeatedly with fetal hydrops due to syphilis, thus dilution of maternal serum to avoid false-negative results is required.

Antibody screens for common fetal infections (toxoplasmosis, other infections, rubella, cytomegalovirus [CMV] infection, and herpes simplex [TORCH]) and more sensitive and specific enzyme-linked immunosorbent assay (ELISA) studies for individual infectious agents have been used for many years. The PCR technique is generally accepted as the criterion standard and should be used whenever possible.

Hemoglobin electrophoresis for alpha-thalassemia heterozygosity has been useful in ethnically at-risk populations.

In regions where ethnic diversity is high, routine screening for fetal hydrops may be preferable to selection based on ethnicity. PCR screens and colorimetric monoclonal antizeta antibody tests for heterozygote alpha-thalassemia have been demonstrated as economically feasible screening procedures.

Maternal serum screening tests (multiple-marker, triple-screen, triple-marker), commonly used if fetal anomaly is suspected, are of uncertain value with fetal hydrops.

In one study, positive screening tests (any of the three used) with only a 60% sensitivity in 19 cases of Turner syndrome distinguished some fetuses with cystic hygroma and/or hydrops from those without. Individual components of these tests were examined separately in several other studies.

Elevated alpha fetoprotein (AFP) levels have been reported in hydrops associated with fetomaternal hemorrhage, umbilical cord hemangioma, polycystic kidneys, and infection with cytomegalovirus (CMV), or (parvovirus); however, AFP levels are similar in babies with Turner syndrome with or without hydrops. Use of AFP screening as an index of fetal aplastic crisis in maternal parvovirus infection has been recommended but is of dubious value because several fetal deaths have been observed with AFP levels within the reference range. Thus, the precise diagnostic value of AFP screening is uncertain because definitive studies are not available.

Low levels of unconjugated estriol (uE3) have been found in a hydropic baby with Smith-Lemli-Opitz syndrome, but the test has not demonstrated value in distinguishing between babies with or without hydrops, and normal levels have been observed in several hydropic deaths.

Human chorionic gonadotropin levels have been reported as significantly elevated in hydrops with sacrococcygeal teratoma, choriocarcinoma, parvovirus, Turner syndrome, and Down syndrome; however, these levels have also been normal in several hydropic fetal deaths related to parvovirus.

In a single study, inhibin-A levels were markedly elevated in 12 fetuses with Turner syndrome with hydrops, and they were reduced significantly in those fetuses without hydrops.

Maternal serum immunoglobulin (Ig) G placental alkaline phosphatase levels are increased with fetal hydrops; the clinical utility of this finding is untested.

Direct invasive sampling studies of fetal amniotic fluid or placental tissues have demonstrated value for definitive diagnosis, monitoring of treatment efficacy, and accurate prognosis in a number of conditions associated with hydrops.

Elevated levels of amniotic fluid bilirubin, as measured by the spectrophotometric extrapolation technique first described by Liley, have been demonstrated to be highly sensitive predictors of the severity of fetal anemia due to isoimmunization.[46]  However, the specificity is somewhat lower because alpha-feto bilirubin levels may also be elevated due to maternal hemoglobinopathy or hepatitis and in association with impaired fetal swallowing due to fetal gastrointestinal obstruction and a number of fetal central nervous system (CNS) disorders.

Reports have suggested the use of ultrasonographic methods to detect fetal anemia; however, routine use of such noninvasive methods is not justified in the absence of definitive evidence of their superior sensitivity and specificity, at less risk, when compared with the standard proven method of amniotic bilirubin analysis.

Direct enzyme assays or biochemical analyses of measurements of levels of specific metabolic products may be indicated in the pregnancy at risk of hydrops because of inborn errors of metabolism.

Such studies may use samples from the mother and father (RBCs, serum, urine, tissue), fetus (skin fibroblast cultures or leukocytes from amniotic fluid, fetal RBCs, white blood cells [WBCs], serum samples from direct cordocentesis, serous effusions), placenta (chorionic villous sampling, placental biopsy), or amniotic fluid.

Examples include biochemical analyses of urine or amniotic for abnormal oligosaccharide, mucopolysaccharide, and sphingolipid metabolites when lysosomal disorders are suspected or determination of amniotic fluid 7-dehydrocholesterol reductase if history and findings suggest Smith-Lemli-Opitz syndrome.

Fetal serum endothelin levels are elevated more than two-fold in recipients; however, these levels are normal in donors with twin-to-twin transfusion syndrome.

Endothelin levels were related to the presence and severity of hydrops in these cases. Changes in fetal serum liver enzymes, particularly alanine transaminase and glutamyl transpeptidase, have been demonstrated to occur following correction of the anemia by fetal transfusion. Whether or not these observations may be of diagnostic or prognostic use is currently untested.

Direct fetal diagnostic studies for parvovirus include histologic staining methods (RBC), digoxigenin-labeled B19.

These include a DNA probe (PCR), and avidin-biotin complex immunohistochemical and immunofluorescent studies, among others. Currently, PCR methods appear to be best, although definitive studies providing sensitivity and specificity are not available.

Karyotyping is always indicated if history or ultrasonography results reveal a constellation of findings consistent with a chromosomal aberration or if maternal or family history is suggestive.

Fetal karyotyping and genetic microarray molecular testing should be conducted in all cases of unexplained nonimmune hydrops fetalis.

Chromosomal analyses may be performed on desquamated fetal epithelial cells in the amniotic fluid, fetal tissue biopsy samples, or placental (fetal tissue) biopsy samples.

An increase in AFP has been observed in almost 1 in 10 (8.4%) genetic amniocenteses; fetal mortality exceeded 1 in 10 (14%) when such AFP elevations occurred. Evidence of fetomaternal bleeding is present in 3 of 4 chorionic villous samplings. Thus, careful weighing of benefit versus risk must be made whenever direct invasive diagnostic methods are considered.

To obtain more precise information concerning the fetal status, direct fetal sampling by cordocentesis (or periumbilical sampling) has been used with increasing frequency.

Acidemia, hypoxemia, and hypercarbia are found in most studies of the fetal acid-base balance and blood-gas status obtained at the time of direct fetal treatment. These results are nonspecific and anticipated and, although they may be of use in immediate management, they are unlikely to be of value in longer-term care of the fetus with hydrops.

Analyses of serous effusion fluids (pleural, pericardial, or ascitic, most commonly) have been of surprisingly little value. For example, lymphocyte counts considered characteristic of congenital chylothorax when found in the newborn infant have been observed in pleural effusions from fetuses with cytomegalovirus (CMV) disease.

Serologic tests for specific infections, hemoglobin or hematocrit measurements, platelet counts, WBC counts and morphologic analyses, specific enzyme analyses, and karyotyping are just a few of the more common measurements obtained. Although this information may be invaluable in specific cases, the use of such invasive methods on a routine basis carries significant risks.

Fetal sampling by cordocentesis is followed by significant bradycardia in almost 1 in 20 samplings (3.8%); of those with such complication, almost two thirds die (61.5%).

Elevated amniotic alkaline phosphatase has been observed in association with fetal hydrops due to Turner syndrome.

Although this is likely to be a nonspecific finding, further study is necessary.

The fetal biophysical profile has been demonstrated to be abnormal in severe hydrops.

Cardiotocographic records obtained 12 hours prior to fetal death demonstrate the absence of short-term and long-term variability, absence of tachycardia, presence of late decelerations, and terminal bradycardia.

Sinusoidal heart-rate patterns have been observed consistently in hydrops associated with severe fetal anemia related to isoimmunization and fetomaternal hemorrhage.

Imaging Studies

Once the possibility of fetal hydrops is considered or suspected, sophisticated and complete fetal imaging studies are an initial absolute necessity. Hydrops is defined by the presence of serous effusions in a fetus with subcutaneous tissue edema. Some authors have distinguished the presence of a single effusion (pleural, peritoneal) as an entity distinct from hydrops; however, more recent evidence suggests that an isolated effusion often (if not usually) progresses to overt fetal hydrops.

Exceptions appear to be isolated chyloperitoneum/ascites (usually associated with obstructive uropathy and, thus, not true hydrops) and pleural or peritoneal effusions that regress spontaneously (see Treatment). Thus, careful, complete, and serial imaging is required to establish the diagnosis and the extent of the hydrops.

Examples of radiographic findings of fetal hydrops are shown in the images below.

Chest radiograph revealing the presence of pleural Chest radiograph revealing the presence of pleural effusion, severe edema, and bilateral chest tubes.
Chest and abdomen radiograph revealing the presenc Chest and abdomen radiograph revealing the presence of severe edema and ascites.
Chest and abdomen radiograph revealing the presenc Chest and abdomen radiograph revealing the presence of severe edema, pleural effusion, and bilateral chest tubes. An umbilical artery catheter, umbilical vein catheter, and endotracheal tube are in place.

The equipment used must be capable of providing high-resolution images at large depth. Linear array transducers are commonly used; however, sector scanners provide better views of the heart and many other structures.

Range-gated Doppler ultrasonography capability is optimal for functional physiologic assessments. Use of high-frequency transvaginal two-dimensional and pulsed-wave/color Doppler flow mapping are particularly promising.

The initial imaging study may provide important clues concerning the origin of the fetal condition. For example, most arrhythmias and anomalies may be detected even in the process of establishing the initial diagnosis. However, in most cases, more complex, serially repeated studies may be required to accurately define the constellation of findings in the fetus.


Specific echocardiographic assessment of fetal cardiac structure and function is required in most cases of fetal hydrops. In conjunction with molecular studies, echocardiography may aid clinicians in predicting outcomes or in therapeutic decision making for fetal anemia.[47] Essential elements of this examination should include definitive results concerning (1) assessment of the biventricular outer dimensions in diastole and of the cardiothoracic ratio, (2) the presence or absence of atrioventricular (AV) valve regurgitation, and (3) the umbilical vessel blood flow velocities and pulsations.

Biventricular diameter in diastole had 100% sensitivity and 86% specificity for detection of cardiac failure in one study. These observations, confirmed by results from several other reports, address the basic underlying pathophysiologic disturbance in the faltering cardiac output of the fetus with hydrops and increased central venous pressure (CVP).

The presence of AV valve regurgitation is a common finding, suggesting right-heart failure or an increased preload. The persistence of serious functional AV valve incompetence following treatment interventions is ominous, particularly in terms of fetal outcome. The proportion of atrial area taken up by the regurgitant jet is related to hydrops, as is the proportion of systolic time during which AV valve insufficiency is demonstrated. In one study, AV valve insufficiency was pansystolic in all fetuses with hydrops.

Several investigators have studied umbilical and fetal abdominal vessel pulsations, flow velocities, and waveforms in hydrops caused by tachyarrhythmias, alpha-thalassemia, and twin-twin transfusion. Because sensitivity, specificity, and predictive measurements are not available, the practical clinical value of these studies is uncertain. However, the results available to date suggest that they may provide valuable quantitative and qualitative pathophysiologic information and may even be predictive of fetal deterioration prior to the development of overt hydrops in some situations.

Umbilical venous (UV) blood flow, normally nonpulsatile, demonstrates pulsatile (or double-pulsatile) flow, a finding consistent with an increased fetal CVP. Pulsed Doppler duplex ultrasonographic studies demonstrate higher UV and inferior vena cava (IVC) blood velocity and blood flow, suggesting an increase in the preload (cardiac) index. Studies of IVC, hepatic vein, and ductus venosus blood flow demonstrate similar results. In hydrops caused by sustained tachycardia, reversal of blood flow (or increased retrograde flow) with systolic forward flow and diastolic reverse flow is present at heart rates exceeding 220 bpm; these abnormalities are reversed by successful fetal treatment with return of the heart rate to 210 bpm or less. Great interindividual differences in the time required for this reversal are observed.

Myocardial function is impaired with hydrops, and the severity of this functional cardiomyopathy is reflected by the degree and persistence of AV valve incompetence and UV catheter (UVC)/IVC flow patterns in the fetus.

Abnormalities in umbilical artery (UA) blood flow are also found. UA early-diastolic blood flow velocity is absent, and end-diastolic UA velocity is reversed. The UA pulsatility index (PI) is increased in fetal-fetal transfusion hydrops and, most importantly, this abnormal finding usually precedes and predicts the development of hydrops in the recipient/hydropic twin. PI also improves parallel to clinical improvement in the fetal condition. Abnormal UA blood flow patterns in alpha-thalassemia hydrops include an increased acceleration slope, more linear decline from maximum systole to end diastole, and reduced spectral broadening; fetal aortic waveforms also demonstrate distorted systolic peaks, flow turbulence, and greatly elevated diastolic frequencies.

Elevated UV pressures, found in approximately two thirds of individuals with fetal hydrops, return to normal with successful treatment. Such measurements, obtained by cordocentesis at time of fetal treatment, may be useful in assessing the success of fetal therapies that require a direct invasive approach.

Other Tests

The 2013 Society of Obstetricians and Gynaecologists of Canada guidelines for the investigation and management of nonimmune fetal hydrops include the following recommendations[39] :

  • All patients with fetal hydrops should be referred promptly to a tertiary care center for evaluation.

  • Fetal chromosome analysis and genetic microarray molecular testing should be offered where available in all cases of nonimmune fetal hydrops.

  • Imaging studies should include comprehensive obstetrical ultrasonography (including arterial and venous fetal Doppler studies) and fetal echocardiography.

  • Investigation for maternal–fetal infections, and alpha-thalassemia in women at risk because of their ethnicity, should be performed in all cases of unexplained fetal hydrops.

  • To evaluate the risk of fetal anemia, Doppler ultrasonographic measurement of the middle cerebral artery peak systolic velocity should be performed in all hydropic fetuses after 16 weeks of gestation. In cases of suspected fetal anemia, fetal blood sampling and intrauterine transfusion should be offered rapidly.

  • All cases of unexplained fetal hydrops should be referred to a medical genetics service. Detailed postnatal evaluation by a medical geneticist should be performed on all cases of newborns with unexplained nonimmune hydrops.

  • Autopsy should be recommended in all cases of fetal or neonatal death or pregnancy termination. Amniotic fluid and/or fetal cells should be stored for future genetic testing.



Medical Care

The diagnosis and management of hydrops fetalis continue to be challenges for perinatologists and neonatologists. Mortality is high, and treatment options are limited. The single most important factor to ensure proper treatment of the fetus with hydrops is a precise and detailed diagnosis. Until the underlying pathophysiology is clearly understood and the extent of the abnormalities leading the development of hydrops is completely defined, any attempt at treatment is futile and potentially harmful.

If prenatally diagnosed, the mother should be referred to a high-risk center for further management and multidisciplinary counseling due to the high risk of fetal demise.[48]  Close coordination between obstetric and neonatal specialists is essential.[36] Prenatal steroids should be administered if preterm delivery is anticipated.

Once the underlying problems are completely understood, address the question of whether the abnormalities present are compatible with life, whether fetal survival would be at the cost of an unacceptably poor quality of life, and what the consequences may be for future pregnancies. Currently, parental involvement and guidance are fundamental requirements and require the full parental knowledge of all the possible potential consequences.

If the decision is made to continue the pregnancy, the next steps are to decide whether to intervene with invasive fetal treatment and to determine at what point preterm delivery represents less risk for the fetus than continued gestation. Because major uncertainties about these questions are inevitable, regardless of the underlying cause, full parental involvement is essential.

Fetal intervention

Possible fetal interventions include fetal transfusion for profound fetal anemia, maternal antiarrhythmic medications (eg, digoxin) for fetal arrhythmia, and in-utero surgery (eg, fetal thoracocentesis/paracentesis, surgical resection).

Decisions about fetal treatment are often uncertain and difficult, because the necessary evidence for a diagnosis as well as for balancing the risks against the benefits of a specific treatment is not available. Although many anecdotal approaches are found in the literature, no properly designed clinical trials are available for the clinician concerned with evidence-based management. Likewise, many treatment schemes are recognized, but all are based on the biases and experiences of the individual authors.

To further complicate the issue, spontaneous remission of the hydropic process has been reported in hundreds of cases. The underlying causes in these cases include cardiac arrhythmias, twin-to-twin transfusion syndrome, pulmonary sequestration, cystic adenomatoid malformation of the lung, lysosomal storage diseases, cystic hygroma with or without Noonan syndrome, parvovirus and cytomegalovirus (CMV) infections, placental chorangioma, and idiopathic ascites or pleural effusions. Clinicians and parents must completely understand that decisions at this are essentially uncertain and arbitrary.

Unproven high-risk treatments are easier to accept when they consist of procedures targeted to correct the underlying pathophysiology leading to fetal hydrops. Thus, the most widely accepted management schemes include fetal transfusion to correct anemia (regardless of cause), drug treatments for cardiac arrhythmias, correction or reduction of space-occupying lesions that impede cardiac venous or lymphatic return, and procedures designed to stop fetal loss of blood, regardless of cause.

Fetal arrhythmias

Treatment options reported for fetal arrhythmias have included doing nothing, administering drugs, and immediate delivery. If fetal maturity permits, the most simple and direct approach is delivery of the affected fetus and direct neonatal treatment of the arrhythmia. When fetal immaturity prevents this approach, use of drugs has generally been accepted as appropriate. However, whether this strategy is justified is not supported by any evidence from controlled clinical trials, and the frequency with which spontaneous cessation of the arrhythmia and remission of the hydrops has been reported should promote more skepticism and caution about fetal drug treatment than generally has been standard.

Drugs have been administered to the mother (oral [PO], intramuscular [IM], intravenous [IV]), to the fetus (intraperitoneal [IP], IM, IV via cordocentesis), and to both, in an attempt to correct the fetal arrhythmias. Even fetal pacing has been reported. As perhaps expected, treatment failures are infrequently reported whereas the successes serve as topics for case or case-series reports (ie, reporting bias). Such treatment is not without risk, partly consequent to the drugs used and not uncommonly related to the mode of administration.

The agents used have included digitalis, furosemide, flecainide, verapamil, amiodarone, propranolol, procainamide, quinidine, adenosine, sotalol, terbutaline, corticosteroids, and immunoglobulins; various combinations of these drugs have also been administered. Although adenosine appears to be particularly effective with supraventricular arrhythmias, and corticosteroid therapy seems effective for complete fetal heart block associated with maternal collagen diseases, the choice of drug remains empiric and arbitrary until such time as definitive evidence from clinical trials becomes available.

The prudent clinician may choose the approach that offers the least risk to the fetus and the mother until more definitive data are available.

Fetal anemia

Intrauterine IP fetal transfusion

The success of intrauterine IP fetal transfusion with packed red blood cells (PRBCs) in the treatment of the severely anemic fetus of an isoimmunized pregnancy has been a modern success story for perinatal medicine. Unfortunately, historic controls form the basis for this conclusion, and definitive evidence from randomized clinical trials will probably never be available.

The use of intrauterine IP fetal transfusion to correct fetal anemia from various other causes (eg, hemorrhage into a twin, from highly vascularized tumor masses, consequent to marrow aplasia with severe fetal infection, hemoglobinopathy) has been reported with many favorable outcomes. Again, whether this is real or a consequence of reporting bias is uncertain. Nevertheless, fetal transfusion using the IP route has apparently become accepted as the standard of care for the fetus with severe anemia.

Intravascular (umbilical vein [UV]) transfusion

A more direct approach has been used with increasing frequency: Intravascular (UV) transfusion of packed RBCs is the treatment of choice for fetal anemia, replacing IP transfusion. Hydrops or fetal anemia (hematocrit [Hct] level <30%) is an indication for UV transfusion in infants with pulmonary immaturity.

Intravascular fetal transfusion is facilitated by maternal and fetal sedation with diazepam and by fetal paralysis with pancuronium. Packed RBCs are given by slow-push infusion after cross-matching with the mother's serum. The cells should be obtained from a CMV-negative donor and irradiated to kill the lymphocytes to avoid graft-versus-host disease. Transfusions should achieve a posttransfusion Hct level of 45%–55% and can be repeated every 3-5 weeks.

Indications for delivery include pulmonary maturity, fetal distress, complications of percutaneous umbilical blood sampling, or 35-37 weeks' gestation.

The survival rate for intrauterine transfusions is 89%; the complication rate is 3%. Complications include rupture of the membranes and preterm delivery, infection, fetal distress requiring emergency cesarean delivery, and perinatal death.

Routes of fetal administration of blood products

Reported routes of fetal administration of blood products have included percutaneous UV, intrahepatic UV, umbilical artery, and various combined approaches. Even intracardiac transfusions have been reported. Success has been claimed with fetal partial packed-cell exchange transfusion, maternal plasmapheresis, maternal promethazine or corticosteroid treatment, fetal IV immunoglobulin (Ig) G, fetal platelet transfusion, and fetal administration of human granulocyte-colony stimulating factor (G-CSF), again using various routes.

The use of more direct invasive methods may seem to increase fetal risk. This may not appear justified in view of the very low risks demonstrated to accompany the IP route. Prudent clinicians may be justified in taking a very cautious approach to these relatively newer therapeutic techniques until such time as definitive evidence is available that the benefit-to-risk ratio of them has improved.

Fetal hemorrhage

Severe hemorrhage from friable, highly vascular tumor masses and acute, massive hemorrhage from one twin to another often result in quick fetal death. Although those who survive may appear to benefit from fetal transfusion, as described above, continued hemorrhage may make such efforts futile. Thus, a more aggressive approach in such conditions may be justified. For example, surprising success has been reported with tumor debulking surgery for the fetus with a sacrococcygeal tumor and with surgical removal of actively bleeding, highly vascularized fetal intraabdominal, thoracic, or placental masses.

Photocoagulation and radiofrequency thermal ablation techniques also demonstrate much promise in this regard. The information is preliminary; most of it comes from animal studies, and no extensive clinical trial experience in the human fetus is currently available. Nevertheless, life-threatening disease may justify life-threatening treatment in some cases, and use of such technology in situations of active fetal hemorrhage may hold considerable promise. Use of these techniques to correct massive arteriovenous shunting causing fetal hydrops also demonstrates their potential effectiveness.

Twin-to-twin transfusion syndrome

The twin-to-twin transfusion syndrome presents a somewhat more puzzling problem. The temptation to transfuse the anemic fetus is apparent in the literature; however, no evidence of overall benefit from this approach exists.

As noted earlier, if one twin has developed hydrops in this situation, the recipient twin develops hydrops, not the donor. Thus, volume reduction in the recipient or combined transfusion/reduction procedures to the twins appears to be more logical but has seldom been used as it does not correct the ongoing pathophysiology.

Feticide of the affected twin has often been reported; however, subsequent development of hydrops in the previously normal twin is also surprisingly commonly reported. Thus, the management of the twin-to-twin transfusion syndrome remains an unresolved problem. Examination of the cauterization of vessels in the placenta that appear to connect the circulation of the twins is ongoing.

Space-occupying masses

Space-occupying masses, which impair venous or lymphatic return, are among the more important causes of fetal hydrops. Management varies depending on the type of lesion and from center to center. However, the fundamental basis for most treatments has been reduction or removal of the mass when immediate delivery is not practical.

Pleural and pericardial effusions and ascites

Pleural effusions have been managed with single or serial fetal thoracenteses, pleurothoraco-amniotic shunts, and direct fetal surgical maneuvers to correct the underlying cause.

Pericardial effusions have been managed similarly with single or serial pericardiocenteses or continuous drainage maneuvers.

Ascites has also been treated with single or multiple taps, peritoneoamniotic shunts, and IP albumin. Successes and failures have been reported with all these methods; there is no evidence to suggest that one approach is any better than another, because proper comparative trial data are not available.

Underlying fetal anomalies

Fetal surgery with definitive correction of the underlying anomaly has been reported with increasing frequency. Improved fetal survival with cystic adenomatoid malformation and with bronchopulmonary sequestration has been observed in several large case series in which these direct corrective measures have been employed. Although this success has been measured against outcomes using historic controls, such measures make physiologic sense and, thus, demonstrate considerable promise.

Perinatal management

Resuscitation and delivery room management of hydrops fetalis pose a unique set of problems for the neonatologist. The obstetrician must work collaboratively with the neonatologist as soon as hydrops is identified in the fetus. Note the following:

  • Once hydrops has been diagnosed antenatally, make every effort to establish the cause; this is helpful in treating the infant at birth. Perform or repeat antenatal ultrasonographic examination to assess the presence and extent of pleural effusion, pericardial effusion, or ascites prior to delivery, because the fluid may require aspiration in the delivery room to establish adequate ventilation and circulation.

  • Assessment of fetal hematocrit, partial pressure of oxygen (pO2), and pH by percutaneous umbilical sampling, although risky, may be helpful in selected cases for early management.

  • In addition to appropriate equipment and supplies, a skilled team of experienced healthcare professionals (neonatologists, nurses, respiratory therapists, radiograph technician, ultrasonography technician) should be present in the delivery room.

  • Inform the blood bank or have type O-negative blood available in the delivery room for immediate transfusion through umbilical catheters. If the fetus is severly anemic, PRBC transfusion can be life saving and may improve the resuscitation outcomes. If blood transfusion is required in the delivey room, before the blood is tranfused, obtain blood samples for a complete blood cell (CBC) count, newborn diagnostic screening, and other laboratory tests.

  • After establishing the infant's airway and ventilation, place umbilical arterial and venous catheters to monitor arterial pressure, blood gases, and venous pressure.

  • PRBCs or whole cross-matched blood should be available for transfusion or partial exchange transfusion to correct severe anemia in the neonatal intensive care unit (NICU).

  • Anticipate and promptly correct metabolic derangements such as acidosis and hypoglycemia.

  • Surfactant deficiency and hypoplastic lungs may be associated with hydrops and are managed accordingly.

  • Drainage of the pleural and abdominal cavities of pleural and ascitic fluid, respectively, may be necessary to adequately ventilate the infant.


Fetal hydrops should be considered a medical emergency that requires urgent referral to a maternal-fetal medicine specialist, allowing for detailed and comprehensive ultrasonographic examination and early identification of any treatable causes. Referral to a geneticist is also essential to plan for additional investigations.

Autopsy should be strongly recommended in all cases of nonimmune fetal hydrops . Fetal blood, tissue, DNA, and amniotic fluid should be collected for storage. The preservation of a potentially dividing fetal cell line (amniocytes, skin biopsy) is indicated for future biochemical or molecular genetic testing. Placental examination (microscopy, histopathology) focusing on tumors, fetal anemia, infection, and metabolic disorder is indicated.[39, 49]



Medication Summary

The number of drugs that have been used for the correction of fetal arrhythmias reflects the amount of uncertainty about dosage, effectiveness, and hazards. Fetal pharmacokinetic studies are not available, and dosage schedules for these very immature infants are uncertain or derived from data on older and bigger infants and children. Thus, consider each case individually; be aware that therapeutic misadventures remain possible if not probable.

Cardiac glycosides

Class Summary

These are used for fetal cardiac failure. Positive inotropic agents (eg, digoxin) increase force of contraction of myocardium and are used to treat acute and chronic CHF. Digoxin may also be used for fetal supraventricular tachycardia (SVT) because it decreases AV conduction.

Digoxin (Lanoxin, Lanoxicaps)

Recommended dosages require considerable modification because of individual variations in sensitivity to drug in adults, children, and (probably) fetuses. Usually administered to mother; thus, adult dosages are used. Transplacental transfer is normally excellent; however, impaired fetal perfusion of placental circulation due to severe cardiac failure results in impaired drug pickup; thus, fetal drug levels may be much lower than maternal concentrations.

Loop diuretics

Class Summary

These are used to treat fetal edema. They promote excretion of water and electrolytes by kidneys and are used to treat heart failure or hepatic, renal, or pulmonary disease when sodium and water retention has resulted in edema or ascites.

Furosemide (Lasix)

Diuretic, in conjunction with digoxin, that has been used in management of fetal hydrops. Both transplacental (maternal administration) and direct fetal routes have been used. No satisfactory pharmacokinetic data are available to support these recommendations.

Antiarrhythmic agents

Class Summary

These agents alter electrophysiologic mechanisms responsible for arrhythmia and are used to treat fetal arrhythmia.

Verapamil (Calan, Calan SR, Covera-HS, Verelan)

Anecdotal use.

Amiodarone (Cordarone)

Limited use in fetus.

Adenosine (Adenocard)

Recent use has been promising; however, most information is in form of case reports.

Procainamide (Procanbid, Pronestyl)

Use in children well established; however, little data available on use in preterm neonate or fetus.

Sotalol (Betapace)

Recent use in fetal arrhythmias has been promising; however, data are scarce, and definitive pharmacokinetic studies have not been performed.

Flecainide (Tambocor)

Limited data from infants suggest that half-life at birth may be prolonged. These data have not been extended backward to fetal life. Maternal (transplacental) use, in conjunction with digoxin, has been promising anecdotally.



Further Inpatient Care

Note the following:

  • If the precipitating cause was profound anemia, red cell survival may remain reduced in patients with isoimmune hemolytic anemia, and red cell production may be impaired in the fetus or newborn who has received multiple red cell transfusions.

  • If the cause of hydrops fetalis was a treatable infection, assurance of total eradication of the offending agent is obviously necessary.

  • In situations in which multiple anomalies and/or chromosomal abnormalities are present, family counseling and consultation with a medical geneticist are recommended.

  • Follow-up measures targeted toward the specific pathophysiologic disturbances present in individual cases may be required (eg, any baby who has experienced a compromised perinatal period).

  • Despite the profound compromise in perfusion and fetal function of multiple organ systems in the fetus with hydrops, the limited follow-up data that are currently available provide an unexpectedly optimistic outlook for babies who survive fetal hydrops.