Umbilical Cord Complications |
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INTRODUCTION | ¡@ |
Umbilical cord complications in pregnancy are numerous, ranging from false knots, which have no clinical significance, to vasa previa, which often leads to fetal death. As prenatal ultrasound 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.
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CORD LENGTH | ¡@ |
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 to the fetal left. Six percent of cords are shorter than 35 cm, and 94% of cords are longer than 80 cm.
Causes of differences in cord length are unknown.
Assessing cord length prenatally is not possible.
Vascular occlusion by thrombi and true knots are more common in extremely long cords; they also have a greater tendency to prolapse through the cervix. In contrast, extremely short cords are more likely to be associated with placental abruption, uterine inversion, oligohydramnios, and breech presentation. They can rupture, with hemorrhage causing fetal exsanguination and death.
Straight cords with few or absent helices have been associated with adverse fetal outcomes.
In cases of placental abruption, oligohydramnios, or breech presentation, special consideration should be given to measurement and documentation of cord length.
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SINGLE UMBILICAL ARTERY | ¡@ |
The umbilical cord normally contains 2 arteries and a single vein. Occasionally, cords have an absence of one umbilical artery, with the left artery absent more commonly than the right. Single umbilical arteries are associated more commonly with fetal anomalies than normal cords.
Single umbilical artery occurs in fewer than 1% of cords in singletons and 5% of cords in at least one twin. Incidence can be underestimated with gross examination of the cord, especially if the portion close to the placenta is examined, because the arteries often fuse close to the placenta.
Single umbilical arteries are found twice as often in white women than in African American and Japanese women. Diabetes increases the risk significantly. Two-vessel cords are found more frequently in fetuses aborted spontaneously. 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 ultrasound. The vein usually is larger than the arteries. The presence of only 2 vessels on an ultrasound cross section is highly suggestive of a single umbilical artery.
Of infants with a single umbilical artery, 20-50% have associated fetal anomalies, including cleft lip, cardiovascular abnormalities (especially ventricular septal defects and conotruncal defects), ventral wall defects, central nervous system defects, esophageal atresia, spina bifida, diaphragmatic hernia, cystic hygroma, hydronephrosis, dysplastic kidneys, polydactyly, syndactyly, and marginal and velamentous insertion of the cord.
With single umbilical arteries, a 20% perinatal mortality rate exists. Two thirds of deaths occur before birth. Of the one third of neonates who die postnatally, most have associated congenital abnormalities. Many of those without overt abnormalities are premature or have intrauterine growth retardation.
Prenatal diagnosis of a single umbilical artery should prompt examination for other anomalies. Echocardiograms may be considered because heart defects are common.
Thirty percent have congenital anomalies, which may include trisomy 13, trisomy 18, and triploidy; trisomy 21 is uncommon.
Because associated anomalies can occur in any organ system, a detailed anatomy survey should be carried out whenever a 2-vessel cord is discovered. If anomalies are found, fetal karyotyping should be considered. Because growth is retarded in 30% of affected fetuses, a third trimester ultrasound for fetal growth should be considered. Twenty percent are delivered prematurely. Perinatal mortality is approximately 20%. Neonatal ultrasound should be used liberally to examine for anomalies.
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VELAMENTOUS INSERTION AND VASA PREVIA | ¡@ |
Velamentous insertion
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 more frequently in 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 can cause hemorrhage if the vessels are torn when the membranes are ruptured and is associated with low birth weight. This condition is accompanied by various anomalies, such as congenital hip dislocation, asymmetrical head shape, spina bifida, esophageal atresia (the most common anomaly associated with this condition), ventricular septal defects, cleft palate, bilobed placenta, low birth weight, and prematurity.
Velamentous insertion is not diagnosed well with ultrasound. The condition is associated with a lower maternal serum a-fetoprotein (AFP) and higher maternal serum human chorionic gonadotropin (HCG).
If detected, the presence of a fetal fluid-filled stomach should be confirmed to rule out esophageal atresia, and an echocardiogram should be considered to rule out ventricular septal defects. Fetal growth may be monitored with ultrasound through the third trimester. Strong consideration should be given to an elective cesarean delivery to avoid a vasa previa rupture if the velamentous insertion is in the lower segment.
Vasa previa
Vasa previa occurs when the fetal vessels in a velamentous insertion, which are not protected by Wharton jelly, or vessels running between the placenta and a succenturiate lobe cross the internal os and become situated in front of the presenting part of the fetus. Vasa previa also may exist over the dividing membrane when a second twin has a velamentous insertion on the membrane.
This condition occurs in 1 per 2000-3000 deliveries.
The cause of vasa previa is unknown.
Vasa previa occasionally may be felt on palpation and may be detected using ultrasound. Color Doppler can be used to visualize the course of the vessels, and pulse Doppler 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 during labor may indicate a ruptured vasa previa. When the source of vaginal bleeding is unknown and is not believed to result from placenta previa or abruption, the Kleihauer-Betke or Apt tests are useful for detecting fetal blood. Massive bleeding can occur with vasa previa.
If compressed, the vessels can cause fetal heart decelerations. The risk of fetal exsanguination is significant if the vessels are torn when the membranes rupture, with an associated 50-75% fetal mortality rate. In monochorionic twins, the first twin may exsanguinate, and the second twin may exsanguinate through interfetal placental anastomoses. Compression of the vessels during labor also can cause the vessels to thrombose.
Cesarean birth is the preferred mode of delivery for known vasa previa after confirming fetal lung maturity and is mandatory if significant vaginal bleeding occurs. Endovaginal color flow Doppler should be considered to rule out vasa previa for patients with a known succenturiate lobe. Vasa previa always should be anticipated with multiple births.
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CORD KNOTS, NUCHAL CORD, AND CORD STRICTURE | ¡@ |
Cord knots
True knots and false knots can form in the umbilical cord. False knots are kinks in the vessels that enable the umbilical vein, which is longer than the umbilical artery, to fit within the length of the cord.
True knots occur in approximately 1% of pregnancies, with the highest rate occurring in monoamnionic twins. False knots are more common.
True knots arise from fetal movements and are more likely to occur during early pregnancy, when more amniotic fluid is present and greater fetal movement occurs.
True knots have been reported to lead to a 6% fetal loss rate, presumably because of compression of the cord vessels when the knot tightens. False knots have no known clinical significance.
Umbilical knots of any kind are not easy to detect on ultrasound imaging.
A cesarean delivery may be considered if a diagnosis of a true cord knot is made.
Nuchal cord
With nuchal cord, the cord becomes 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.
One loop around the neck occurs in approximately 20% of cases, and multiple loops occur in fewer than 2 per 1000 cases.
This can be detected using color Doppler ultrasound, with a sensitivity of over 90% after 36 weeks of gestation.
Nuchal cords rarely cause fetal demise and are not intrinsic reasons for intervention.
The prenatal treatment of nuchal cord is controversial. Fetal testing and Doppler studies of the cord may be instituted. As the fetus descends during labor, the cord may become compressed, leading to fetal heart rate decelerations. Infants with nuchal cords tend to have more decelerations in labor and lower umbilical artery pH.
Cord stricture
Cord stricture is constriction or occlusion of the cord.
This condition occurs in 1 per 250 deliveries.
Localized deficiencies in development of Wharton jelly cause weaknesses in the cord, about which the fetus can rotate and cause torsion. The site of torsion usually is near the fetus. Edema is usually present distal to the area or areas (multiple strictures can occur) affected.
This condition cannot be diagnosed using ultrasound. The following anomalies have been reported with constriction of the cord:
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Most infants with cord stricture are stillborn.
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CORD HEMATOMA, CORD CYSTS, AND CORD VARIX | ¡@ |
Cord hematoma
A cord hematoma is extravasation of blood into the surrounding Wharton jelly.
This condition occurs in 1 per 5,000-13,000 deliveries.
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 also can cause hematomas. Cord hematoma also can also occur spontaneously and in association with cord cysts. The vein-to-artery ratio is 1:9.
Fifty percent of fetuses with umbilical hematomas die. Cord hematoma is a diagnosis of exclusion for fetal death. Cord thrombosis can occur, with extension into the fetal aorta in cases involving the artery or leading to fetal demise in cases involving the umbilical vein. Thromboses have been associated with nonimmune hydrops. Only 4 reports exist of infants surviving thromboses of the umbilical vein.
Doppler studies can evaluate a suspected hematoma, which increases vascular resistance.
If the diagnosis of cord hematoma is confirmed, an amniocentesis may be performed, and delivery can be undertaken when the fetus is documented to be mature.
Cord cysts
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 3% 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's 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 found most commonly at the fetal end of the cord. Pseudocysts are associated with chromosomal anomalies, omphalocele, and hemangiomas. Of cord cysts of any type, 20% are associated with structural or chromosomal anomalies. The longer the cyst persists, the more likely it is to be associated with an anomaly.
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 during the first trimester, when the umbilical vessels are small.
Persistent cysts may be observed with fetal karyotyping and level 2 second trimester ultrasound. In patients with large cysts, delivery may be undertaken as soon as fetal lung maturity is achieved.
Cord varix
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.
Several reports have documented poor fetal outcomes in the presence of varices thought to be due to the vascular steal effect of the structure.
Once detected, regular fetal testing and third trimester interval growth studies may be considered.
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HEMANGIOMAS AND TERATOMAS | ¡@ |
Hemangiomas
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 hyperechogenic mass in the cord is detected with ultrasound.
These tumors can shorten or compromise the vasculature, or they can obstruct the cord. In addition, angiomas can precipitate tricuspid regurgitation, with atrial enlargement and associated cardiac failure and hydrops. AFP levels tend to be high with angiomas.
The presence of a cord tumor requires monitoring for interval growth, fetal hydrops, and fetal well being throughout pregnancy. Tumors cause umbilical vessel constriction, which may be monitored with Doppler flow studies.
Teratomas
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 evaginates 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 diagnosed prenatally.
Obstetric management involves monitoring for vascular compression by an enlarging tumor by observing growth and possible development of hydrops that can lead to fetal death.
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CORD PROLAPSE | ¡@ |
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 3% of deliveries in the vertex position and in 3.7% of deliveries in the breech position. The risk is increased further 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. 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 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.
Evaluate the position of the cord in patients who are at risk for prolapsed cord. In patients with intact membranes, cesarean delivery is recommended for term pregnancies. In preterm infants, a course of expectant management with serial examinations should be pursued.
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BIBLIOGRAPHY | ¡@ |