Introduction
Background
Polyhydramnios is the presence of excess amniotic fluid in the uterus. By definition, polyhydramnios is diagnosed if the deepest vertical pool is more than 8 cm or amniotic fluid index (AFI) is more than 95th percentile for the corresponding gestational age.
Polyhydramnios.
Graph illustrating amniotic fluid index in a normal singleton pregnancy. The solid line is the mean AFI, the lower dotted line is the 5th percentile value, and the upper dotted line is the 95th percentile value (data adapted from Moore, 1990). Image courtesy of Christopher L. Sistrom, MD.
Polyhydramnios has a variety of causes affecting the mother or the fetus. The presence of polyhydramnios should prompt a search for other fetal anomalies. Some of the anomalies can be diagnosed with sonography, while others require karyotyping.
Pathophysiology
Polyhydramnios can be caused by increased production of amniotic fluid, decreased absorption of amniotic fluid, or other causes.
The etiologic factors are categorized as follows: (1) maternal causes, (2), intrinsic or extrinsic obstruction of the gastrointestinal tract, (3) neurologic and neuromuscular problems impairing swallowing, (4) fetal polyuria, (5) high-output congestive cardiac failure, (6) congenital infection, (7) idiopathic causes,1 and (8) skeletal dysplasias and syndrome.
Causes of polyhydramnios include the following: diabetes mellitus, hydrops fetalis, esophageal atresia, duodenal atresia/stenosis, gastroschisis, diaphragmatic hernia, thoracic and mediastinal masses, anencephaly, muscular dystrophy, myotonic dystrophy, chromosomal anomalies (eg, trisomy 21), cardiovascular diseases, skeletal dysplasias (including achondroplasia), neuromuscular anomalies, severe fetal anemia, sacrococcygeal teratomaplacental chorioangioma, placental arteriovenous fistula, congenital syphilis, viral hepatitis, diabetes insipidus, twin-twin transfusion syndrome,2 idiopathic causes, maternal substance abuse,3 Beckwith-Wiedemann syndrome,4 and Pena-Shakir syndrome.5
In anencephaly, polyhydramnios is believed to be due to impaired swallowing secondary to absence of brain or fluid transudation across the meninges. Another cause is vasopressin deficiency producing polyuria.
Acute hydramnios
Acute hydramnios is a subtype of hydramnios in which amniotic fluid rapidly accumulates, producing severe symptoms in the mother.6 Clinically, the size of the fundus increases rapidly at a rate of more than 1 cm/d.Acute hydramnios typically occurs in twin-twin transfusion syndrome, where the recipient twin is affected. The common clinical differential diagnosis is abruptio placentae.
Idiopathic hydramnios
Idiopathic hydramnios is a diagnosis of exclusion when no other cause of polyhydramnios can be identified. The cause is identified in 75-91% of cases when the deepest pocket is more than 12 cm. The cause is identified in 17-29% of cases when the deepest pocket is 8-12 cm.
Frequency
United States
With a deep pocket of 8 cm as criteria of polyhydramnios, the incidence is 1-3% of all pregnancies. About 20% are associated with fetal anomalies.
Mortality/Morbidity
Adverse effects of polyhydramnios include abdominal swelling, abdominal discomfort, uterine irritability, postpartum hemorrhage, difficulty in respiration due to an elevated diaphragm, ureteric obstruction, preeclampsia, sudden rupture (increased incidence of abruptio placentae and unstable lie), preterm labor (common if caused by congenital anomalies), congenital malformations, premature rupture of the membranes, asphyxia, cord prolapse, abruptio placentae, placental insufficiency, and high intra-amniotic pressure.
- With preterm labor, the perinatal mortality rate is 10-30%. The rate is 87% in anomalous fetuses and 13% in idiopathic cases.
- High intra-amniotic pressure causes impaired uteroplacental perfusion, which can cause fetal hypoxemia and acidemia, which accounts for the 6-10% of deaths that occur in normally formed fetuses.
Anatomy
Amniotic fluid is an ultrafiltrate of maternal plasma in the first trimester and an ultrafiltrate of fetal plasma through the fetal skin in second trimester. It also contains fetal urine and lung fluid after 20 weeks. Hence, up to 20 weeks, amniotic fluid has only plasma components and desquamated fetal skin cells; however, after 20 weeks, it contains urea, creatinine, uric acid, desquamated fetal cells, vernix, and lanugo. It also has pulmonary fluid and fluid filtering through the placenta.
The volume of amniotic fluid progressively increases between 14 and 31 weeks and then decreases. However, with use of single deepest pocket/2-dimensional technique, it progressively increases between 14 and 20 weeks, reaches a plateau between 20 and 37 weeks, and then decreases.
On average, the volume of amniotic fluid increases at the rate of 10 mL/wk from 8 weeks and at the rate of 60 mL/wk from 21 weeks on, followed by a decline by 33 weeks. The normal volume is 50 mL at 12 weeks, 400 mL at mid pregnancy and 1000 mL at term. The osmolality of the amniotic fluid progressively decreases with gestational age.
Amniotic fluid has multiple functions. It cushions the developing fetus, protecting it from trauma, and it provides a closed environment for its proper development. Amniotic fluid also contains growth factors necessary for normal development of the fetus, its gastrointestinal tract, and lungs. The fluid is also involved in nutritional function and maintaining the temperature.
Presentation
Polyhydramnios manifests as abdominal swelling out of proportion to the gestational age, with abdominal discomfort
On physical examination, the abdomen is distended out of proportion to the gestational age, the symphysiofundal height is increased, the abdomen is tense and tender, and fetal parts are difficult to palpate.
Clinical management of polyhydramnios
Mild polyhydramnios is treated with expectant management.
Indomethacin works by reducing urine production and hence is useful in situations involving fetal polyuria. However, indomethacin is not used in twin-transfusion syndrome or after 35 weeks because the risk of complications increases in these settings. Complications of indomethacin therapy include premature closure of ductus arteriosus, impairment of renal function, and cerebral vasoconstriction.
Amniocentesis is performed when indomethacin is contraindicated, in severe hydramnios, or in symptomatic cases. Amniocentesis is contraindicated when chorioamniotis is present, when the membranes rupture prematurely or are detached, or when abruptio placentae occurs.
Other problem to consider: chorioangioma
Chorioangioma is a highly vascular placental mass that forms as a result of excess capillary formation and the absence of villus differentiation in chorionic tissue.
Three histologic types are described: angiomatous (most common), cellular, and degenerative.
The incidence of chorioangioma is 1 case per 3500-9000 births. Most chorioangiomas are smaller than 5 cm (in 1% of placentas) and asymptomatic. Chorioangiomas larger than 5 cm can produce complications including polyhydramnios, preeclampsia, preterm delivery, congenital malformation, congestive cardiac failure, antepartum hemorrhage, intrauterine growth retardation, and microangiopathic hemolytic anemia.
Sonograms show a placental mass with anechoic spaces, which demonstrate flow on color Doppler studies and pulsatile flow on spectral Doppler trace studies.
Preferred Examination
The diagnostic approach to polyhydramnios consists of the following steps: (1) physical examination of the mother with an investigation for diabetes mellitus, diabetes insipidus, and Rh isoimmunization; (2) sonographic confirmation of polyhydramnios and assessment of the fetus; (3) fetal karyotyping; and (4) maternal serologic testing for syphilis.
Limitations of Techniques
Clinical examination can reveal a uterine size larger than that expected for the corresponding gestational age of the fetus.
Ultrasonography is the most reliable method for diagnosing and quantifying polyhydramnios. Experienced operators make the diagnosis on the basis of subjective assessment. The height of the deepest pocket and the AFI are objective, semiquantitative measurements of the amniotic fluid.
MRI is not necessary for the diagnosis of polyhydramnios, but polyhydramnios can be detected during MRI for other indications. Three limitations of MRI are notable. First, MRI is not cost effective. Second, it is time consuming. For example, the time required for magnetic resonance volumetry can be as long as 6 hours, which is not ideal when sonography can be performed in only a few minutes. Third, MRI requires knowledge of computers and postprocessing.
Differential Diagnoses
Other Problems to Be Considered
Chorioangioma
More on Polyhydramnios |
 Overview: Polyhydramnios |
| Imaging: Polyhydramnios |
| Multimedia: Polyhydramnios |
| References |
| Further Reading |
| Next Page » |
References
Dorleijn DM, Cohen-Overbeek TE, Groenendaal F, Bruinse HW, Stoutenbeek P. Idiopathic polyhydramnios and postnatal findings. J Matern Fetal Neonatal Med. Dec 13 2008;1-6. [Medline].
Wong HS, Kidd A, Zuccollo J, Parker S, Richardson V, Tait J, et al. A Case of Amyoplasia in a Monochorionic Twin Pregnancy: A Sequela from Twin-Twin Transfusion Syndrome?. Fetal Diagn Ther. Jan 20 2009;25(1):31-35. [Medline].
Panting-Kemp A, Nguyen T, Castro L. Substance abuse and polyhydramnios. Am J Obstet Gynecol. Sep 2002;187(3):602-5.
Wilkins-Haug L, Porter A, Hawley P, Benson CB. Isolated fetal omphalocele, Beckwith-Wiedemann syndrome, and assisted reproductive technologies. Birth Defects Res A Clin Mol Teratol. Jan 2009;85(1):58-62. [Medline].
Senocak EU, Oguz KK, Haliloglu G, Karcaaltincaba D, Akata D, Kandemir O. Prenatal diagnosis of Pena-Shokeir syndrome phenotype by ultrasonography and MR imaging. Pediatr Radiol. Feb 5 2009;[Medline].
Queenan JT, Gadow EC. Polyhydramnios: chronic versus acute. Am J Obstet Gynecol. Oct 1 1970;108(3):349-55. [Medline].
Kubik-Huch RA, Wildermuth S, Cettuzzi L, et al. Fetus and uteroplacental unit: fast MR imaging with three-dimensional reconstruction and volumetry--feasibility study. Radiology. May 2001;219(2):567-73. [Medline].
Alfirevic Z, Luckas M, Walkinshaw SA, et al. A randomised comparison between amniotic fluid index and maximum pool depth in the monitoring of post-term pregnancy. Br J Obstet Gynaecol. Feb 1997;104(2):207-11. [Medline].
Magann EF, Sanderson M, Martin JN, Chauhan S. The amniotic fluid index, single deepest pocket, and two-diameter pocket in normal human pregnancy. Am J Obstet Gynecol. Jun 2000;182(6):1581-8. [Medline].
Magann EF, Doherty DA, Chauhan SP, et al. How well do the amniotic fluid index and single deepest pocket indices (below the 3rd and 5th and above the 95th and 97th percentiles) predict oligohydramnios and hydramnios?. Am J Obstet Gynecol. Jan 2004;190(1):164-9.
Moore TR, Cayle JE. The amniotic fluid index in normal human pregnancy. Am J Obstet Gynecol. May 1990;162(5):1168-73. [Medline].
Kirshon B. Fetal urine output in hydramnios. Obstet Gynecol. Feb 1989;73(2):240-2. [Medline].
Engineer N, O'Donoghue K, Wimalasundera RC, Fisk NM. The effect of polyhydramnios on cervical length in twins: a controlled intervention study in complicated monochorionic pregnancies. PLoS ONE. 2008;3(12):e3834. [Medline].
Further Reading
Related eMedicine topics
Polyhydramnios and Oligohydramnios
Oligohydramnios
Clinical trials
Syringe or Continuous Amnioreduction for Symptomatic Polyhydramnios. A Prospective Randomized Study.
Sonographic Assessment of Fetal Deglutition Associated With Hydramnion:Its Absence is Indicative of Central Nervous System (CNS) Pathology
Keywords
polyhydramnios, excess amniotic fluid, acute hydramnios, idiopathic hydramnios, macrosomia, impaired swallowing, amniotic fluid index, AFI, chorioangioma
