Umbilical cord abnormalities are numerous, ranging from false knots, which have no clinical significance, to vasa previa, which often leads to fetal death. As prenatal ultrasonography becomes increasingly sophisticated, many of these conditions are being diagnosed in utero. However, many are not apparent before delivery, and the only forewarning is related to their association with certain conditions such as monochorionic twins and placental abruption.
This article outlines the risk factors for known umbilical cord complications and the available courses of action to avert their associated morbidity and mortality.
The length of the umbilical cord varies from no cord (achordia) to 300 cm, with diameters up to 3 cm. Umbilical cords are helical in nature, with as many as 380 helices. An average umbilical cord is 55 cm long, with a diameter of 1-2 cm and 11 helices.  For unknown reasons, most cords coil to the left.  About 5% of cords are shorter than 35 cm, and another 5% are longer than 80 cm. 
Causes of differences in cord length are unknown  ; however, the length of the cord is thought to reflect movement of the fetus in utero. Specific cell type differences in protein expression patterns of several genes related to cell proliferation may also have a contributory role in cord length anomalies. 
Short cords are associated with fetal movement disorders and intrauterine constraint, as well as placental abruption, cord rupture, and emergent cesarean deliveries (ECDs) for nonreassuring fetal heart rate (NRFHR).  Although short cords have been blamed for the inability of some fetuses to deliver vaginally, available data suggest that vaginal delivery can take place with cords as short as 13 cm,  which is much shorter than the normal range. Excessively long cords are associated with fetal entanglement, true knots, and thrombi. [1, 7]
Assessing cord length prenatally is not possible.
Both increased or decreased umbilical cord coiling has been associated with abnormal outcomes, although some publications suggest that in unselected populations, the degree of coiling is not significant.  In addition, the direction of coiling has been studied, although the data are not extensive, rightward coiling may be associated with a higher risk. 
In cases of placental abruption, oligohydramnios, or breech presentation, consideration may be given to measurement and documentation of cord length after birth, because an abnormal cord length argues for a long-term fetal condition.
In a twin gestation study, umbilical cord coiling was not associated with zygosity (ie, coiling did not appear to be genetically influenced by zygosity). 
Single Umbilical Artery
The umbilical cord normally contains two arteries and a single vein. Occasionally, one umbilical artery is absent, with the left artery absent more commonly than the right. Single umbilical arteries are associated more commonly with fetal anomalies than normal umbilical cords.
Single umbilical artery occurs in fewer than 1% of cords in singletons and 5% of cords in at least one twin. Single umbilical artery also occurs more often in fetal demise than in live births,  and there appears to be an association between isolated single umbilical artery and an increased risk for small-for-gestational-age (SGA) infants and pregnancy-induced hypertension (but not for spontaneous preterm birth).  The incidence can be overestimated with gross examination of the cord, especially if the portion close to the placenta is examined, because the arteries may fuse close to the placenta. 
Single umbilical arteries are found twice as often in white women than in black and Japanese women. Diabetes increases the risk significantly. The male-to-female ratio is 0.85:1.
Single umbilical artery is believed to be caused by atrophy of a previously normal artery, presence of the original artery of the body stalk, or agenesis of one of the umbilical arteries.
The vessels in the cord are clearly identifiable with ultrasonography. The vein is usually larger than the arteries. Single umbilical artery may be diagnosed prenatally with the finding of only 2 vessels on a cross section of the cord, or a vessel seen on only 1 side of the fetal bladder.
Of infants with a single umbilical artery, 20% or more are reported to have associated fetal anomalies,  including cardiovascular abnormalities, gastrointestinal (GI) defects, esophageal atresia, a variety of renal defects, and multiple anomaly syndromes. [14, 15] These anomalies appear to be more common when the right umbilical artery was absent.  The association with fetal defects is more striking in series reported from prenatal diagnosis than in newborn studies; this difference may be due to prenatal diagnosis occurring in a selected, high-risk population. In addition, almost 20% of cases of single umbilical artery diagnosed prenatally in a high-risk population were associated with chromosomal anomalies.  Trisomy 18 is the chromosomal anomaly most highly associated with single umbilical artery.
With single umbilical arteries, a 5-20% perinatal mortality rate has been reported, [18, 19, 20] although this includes fetuses with severe congenital anomalies and chromosomal defects. Two thirds of deaths occur before birth. Of the one third of neonates who die postnatally, most have associated congenital abnormalities. In pregnancies in which no fetal abnormality is found, the incidence of fetal growth restriction and small placental size is increased. [20, 21]
Prenatal diagnosis of a single umbilical artery should prompt examination for other anomalies. Because associated anomalies can occur in any organ system, consider a detailed anatomy survey whenever a two-vessel cord is discovered. Fetal echocardiogram may also be helpful. Consider fetal karyotyping, especially if anomalies are found. Because some studies have reported an association with fetal growth retardation, consider third trimester ultrasonography for fetal growth.  Consider neonatal ultrasonography to examine for renal anomalies.
Velamentous Insertion and Vasa Previa
With velamentous insertion, the umbilical cord inserts into the chorion laeve at a point away from the placental edge, and the vessels pass to the placenta across the surface of the membranes between the amnion and the chorion.
One percent of singletons have velamentous insertion; however, this condition occurs in almost 15% of monochorionic twins  and is common in triplets.
Velamentous insertion occurs (1) when placental tissue grows laterally, leaving the centrally located umbilical cord in an area that becomes atrophic, or (2) when the cord implants in the trophoblast anterior to the decidua capsularis rather than the trophoblast tissue that is destined to become the placental mass.
Velamentous insertion has been diagnosed by ultrasonography with a sensitivity of 67% and specificity of 100% in the second trimester;  first trimester diagnosis is also possible.  The condition is associated with a lower maternal serum alpha-fetoprotein (AFP) and higher maternal serum human chorionic gonadotropin (hCG). [25, 26]
Velamentous insertion can cause hemorrhage if the vessels are torn when the membranes are ruptured, most often with a vasa previa (see below). Velamentous insertion of the cord is associated with low birth weight, prematurity, and abnormal fetal heart patterns in labor, [27, 28] as well as hypoxic ischemic encephalopathy (HIE) of the newborn.  If detected, fetal growth may be monitored with ultrasonography in the third trimester. Consider an elective cesarean delivery to avoid a vasa previa rupture or fetal distress if the velamentous insertion is in the lower segment. 
Vasa previa occurs when the fetal vessels in the membrane are situated in front of the presenting part of the fetus. This may occur because of a velamentous insertion of the cord or with vessels running between the placenta and a succenturiate lobe. Vasa previa may also exist over the dividing membrane when a second twin has a velamentous insertion of the umbilical cord.
This condition is usually said to occur in 1 in 2000-3000 deliveries, although a recent publication quoted a higher risk of 1 in 365 deliveries based on ultrasonographic diagnosis. 
The cause of vasa previa is unknown. Vasa previa may be associated with low-lying placenta, placenta with accessory lobes, and with multiple pregnancies. 
Vasa previa occasionally may be felt on palpation and ultrasonographic detection has been reported. [32, 33] Color Doppler ultrasonography can be used to visualize the course of the vessels, and pulse Doppler ultrasonography can be used to confirm the fetal origin. A series of gray lines in the vicinity of the internal os may be diagnostic of vasa previa. A sinusoidal fetal heart pattern, fetal bradycardia, or fetal heart rate decelerations during labor may all indicate a ruptured vasa previa.  A Kleihauer-Betke test may detect the presence of fetal cells in the vaginal discharge; however, in the face of a ruptured vasa previa, fetal compromise is usually apparent before the test results become available.
The risk of fetal exsanguination is significant if the vessels are torn when the membranes rupture, with an associated 50-75% fetal mortality rate. If compressed during labor, the vessels can cause fetal heart decelerations. Compression of the vessels during labor can also cause the vessels to thrombose.
Cesarean delivery is the preferred mode of delivery for known vasa previa after confirming fetal lung maturity and is mandatory if significant vaginal bleeding occurs.  Prenatal diagnosis of vasa previa can markedly improve outcome. In one report, pregnancies diagnosed prenatally had a 97% fetal survival as compared with 48% in those not diagnosed prenatally.  Consider endovaginal color flow Doppler ultrasonography to rule out vasa previa for patients with a known succenturiate lobe or velamentous insertion of the cord.
Cord Knots, Nuchal Cord, and Cord Stricture
True knots and false knots can form in the umbilical cord. True knots occur in approximately 1% of pregnancies, with the highest rate occurring in monoamnionic twins. False knots (kinks in the umbilical cord vessels) are more common and have no known clinical significance.
True knots arise from fetal movements and are more likely to develop during early pregnancy, when relatively more amniotic fluid is present and greater fetal movement occurs. True knots are also associated with advanced maternal age, multiparity, and long umbilical cords.
True knots have been reported to lead to a 4-fold increase in fetal loss, presumably because of compression of the cord vessels when the knot tightens. Weiner et al noted that umbilical cord entanglements, true knots, and short cords were more common in emergent cesarean deliveries (ECDs) for nonreassuring fetal heart rate (NRFHR) than in vaginal deliveries. 
A cesarean delivery may be considered if a diagnosis of a true cord knot is made. The usefulness of antenatal testing in the followup of pregnancies with this condition is uncertain. 
The cord may become coiled around various parts of the body of the fetus, usually around the neck. Nuchal cord is caused by movement of the fetus through a loop of cord.
Nuchal cord has been associated with labor induction and augmentation, prolonged second stage of labor, and fetal heart rate abnormalities. One report has described a decrease in umbilical cord pH at delivery with nuchal cord, but the difference found (7.32 vs 7.30) does not appear to be clinically significant.  Nuchal cord can be detected using color Doppler ultrasonography, with a sensitivity of over 90%.  Nuchal cords rarely cause fetal demise and are not intrinsic reasons for intervention. [38, 41] Given the minor decrease in pH, fetal monitoring in labor would appear to be prudent, but no data are available to address this issue.
Cord stricture is constriction or occlusion of the cord.
The etiology of umbilical cord stricture is unknown. There is a deficiency in Wharton jelly in the umbilical cord in the area of stricture, however this could be a postmorbid change.
This condition cannot be diagnosed prenatally.
Most infants with cord stricture are stillborn.
Cord Hematoma, Cord Ulceration, Cord Cysts, and Cord Varix
A cord hematoma is extravasation of blood into the Wharton jelly surrounding the umbilical cord vessels.
This condition is rare in live-born infants.
Cord hematoma can occur after the rupture of a varix of the umbilical vein, with subsequent effusion of blood into the cord. Invasive prenatal procedures can also cause hematomas. Finally, cord hematoma can occur spontaneously and in association with cord cysts. The vein-to-artery ratio is 1:9.
Cord hematoma has been described as a cause of acute fetal distress. [44, 45, 46] A more chronic presentation of a cord hematoma may appear as a mass in the umbilical cord. Doppler studies can evaluate a suspected hematoma, which increases vascular resistance. 
If the diagnosis of cord hematoma is confirmed with a stable fetus, an amniocentesis may be performed, and delivery can be undertaken when the fetus is documented to be mature.
Ulceration of the umbilical cord has been described with perforation of the vessels and intrauterine hemorrhage. [48, 49] This complication is rare. The cause of cord ulceration is unknown, although it has been described most often in association with fetal upper intestinal atresias. [48, 50, 51] Umbilical cord ulceration has not been diagnosed prenatally. No evidence suggests appropriate prenatal management.
Cord cysts can be defined as true or false cysts, and they can occur at any location along the cord. They are irregular in shape and are located between the vessels.
Cysts are found in 0.4% of pregnancies. 
True cysts are small remnants of the allantois (ie, allantoid cysts) or the umbilical vesicle. Cysts have an epithelial lining, occur at the fetal end of the cord, and usually resolve during the first trimester. True cysts can be associated with hydronephrosis, patent urachus,  omphalocele,  and Meckel diverticulum. False cysts can be as large as 6 cm and represent liquefaction of Wharton jelly. They do not have an epithelial lining and are most commonly found at the fetal end of the cord. Pseudocysts are associated with chromosomal anomalies, omphalocele, and patent urachus.  Of cord cysts of any type, 20% are associated with structural or chromosomal anomalies.
During fetal anatomy scans, the abdominal wall near the cord insertion is the most likely location to detect a cyst. Cysts can be visualized most easily with color Doppler studies during the first trimester, when the umbilical vessels are small.
Persistent cysts may be observed with fetal karyotyping and level 2 second trimester ultrasonography. In patients with large cysts, cesarean delivery undertaken as soon as fetal lung maturity is achieved may help to avoid fetal damage from cyst rupture during labor. [55, 56, 57]
Cord varix is a cystic dilatation that can occur in any portion of the umbilical vein.
Cord varix rarely occurs, and its cause is unknown.
Color Doppler flow studies show very turbulent flow through the cyst, which is continuous with the umbilical vein.
Reports have documented poor fetal outcomes in the presence of varices and an association with fetal anomalies  and with emergent Cesarean delivery.  Once detected, regular fetal testing, third trimester interval growth studies, and karyotyping may be considered. Some authors have recommended elective delivery when the fetus is mature because of the high risk of fetal distress. 
Hemangiomas and Teratomas
Hemangiomas are hyperechogenic masses that are found mainly at the placental end of the cord.
Hemangiomas rarely occur.
Hemangiomas are tumors of the endothelial cells of the vessels of the umbilical cord. They can be up to 15 cm in diameter and consist of a nodule of endothelial cells surrounded by edema and degenerated Wharton jelly.
A fusiform mass in the cord may be visible with ultrasonography, but the appearance is not specific for hemangioma.
In the presence of a suspected cord tumor, monitoring for interval growth, fetal hydrops, and fetal well-being throughout pregnancy should be considered. As cord tumors cannot be reliably distinguished prior to delivery, monitoring for vascular compression by an enlarging tumor may also be of benefit, although this complication is not associated with hemangioma per se.
Teratomas are germ cell tumors that are found at any location along the cord and have structures derived from all 3 germ cell layers.
Teratomas are rare. 
They arise from germ cells in the wall of the gut that evaginate into the umbilical cord.
Teratomas are differentiated from an acardiac twin because an acardiac twin has some recognizable anatomic structures, whereas the teratoma is totally disorganized.
This condition cannot be specifically diagnosed prenatally. Ultrasonography may reveal an umbilical cord mass. 
Obstetric management for an umbilical cord tumor is described above.
If the umbilical cord presents in front of the fetal presenting part and the membranes rupture, the risk that the cord will prolapse through the cervix into the vagina is significant. Occult prolapse occurs when the cord lies alongside the presenting part.
Cord prolapse occurs in 0.6% of deliveries. The risk is increased with fetal malpresentations, especially when the presenting part does not fill the lower uterine segment, as is the case with incomplete breech presentations (5-10%), premature infants, and multiparous women. 
Causes include abnormal presentation, a long umbilical cord, polyhydramnios, prematurity, and an unengaged presenting part.
Loops of cord in front of the presenting part can be visualized using color Doppler studies. During the course of labor, fetal bradycardia may indicate compression of a prolapsed cord, which should be ruled out with a vaginal examination.
In the presence of intact membranes, the prolapsed cord may resolve spontaneously or may be reduced by the presenting part at the onset of labor. In some cases, manual reduction of the cord has been reported with vaginal delivery and a good fetal result. In the presence of ruptured membranes, a cord prolapse can cause an obstetrical emergency requiring an immediate vaginal delivery or a cesarean delivery at the first sign of fetal distress.