Version May 2024
INTRODUCTION — Structural abnormalities of the umbilical cord may be identified during a prenatal ultrasound examination. This topic will describe several such abnormalities, as well as their potential clinical significance and management of affected pregnancies. Findings on postnatal examination of the umbilical cord and their clinical significance are reviewed separately.
●(See "Gross examination of the placenta", section on 'Umbilical cord'.)
●(See "The placental pathology report", section on 'Umbilical cord'.)
NORMAL UMBILICAL CORD ANATOMY — The umbilical cord contains two arteries and one vein surrounded by a gelatinous stroma (ie, Wharton's jelly) and covered by a single layer of amnion. The arteries carry deoxygenated blood from the fetus to the placenta, and the vein carries oxygenated blood from the placenta to the fetus. Arterial blood flow is pulsatile, with a smaller pulse in the umbilical vein [1]. The physical dimensions of the cord correlate with fetus size.
●Arteries – The left and right umbilical arteries are branches of the left and right internal iliac arteries, respectively. In the pelvis, the two arteries are separated by the bladder but then lie adjacent to each other at the umbilicus, where they exit the fetus and enter the umbilical cord (figure 1). The arteries follow a helical course around the umbilical vein until reaching the placenta, where they separate again and form the chorionic arteries on the surface of the placenta, with perforating branches to the underlying villi (figure 2).
●Vein – The confluence of chorionic veins at the chorionic plate form a single ("left") umbilical vein, which courses through the cord to the umbilicus. Upon entering the fetal abdomen, it runs cephalad until it enters the liver, where it anastomoses with the portal sinus (ie, confluence of portal veins) and the ductus venosus (figure 1) [2].
A "right" umbilical vein is present very early in embryogenesis and then usually degenerates. Rarely, it persists as the only umbilical vein [3,4] or as a fourth umbilical vessel. (See 'Supernumerary vessels' below.)
After birth, the intraabdominal portions of the umbilical vessels degenerate; the umbilical arteries become the lateral ligaments of the bladder, and the umbilical vein develops into the round ligament of the liver.
ULTRASOUND EXAMINATION OF THE UMBILICAL CORD
Second-trimester examination
Standard second- and third-trimester examination — The American Institute of Ultrasound in Medicine (AIUM) practice parameter for the standard second- and third-trimester ultrasound examination includes imaging the umbilical cord to (1) determine the number of vessels and (2) assess the fetal and placental insertion sites [5].
The two arteries and vein can be seen clearly in both the transverse and longitudinal planes using conventional two-dimensional imaging techniques (image 1). The umbilical arteries have smaller diameters than the vein and usually loop around it.
Color Doppler improves visualization of the umbilical vessels; three-dimensional imaging techniques may also be used to enhance image quality [6-11].
Expanded second- and third-trimester examination — The author performs a more extensive examination than the standard examination described above. It includes assessment of the helical pattern of the umbilical arteries and amount of Wharton's jelly [12]. The author also routinely uses color Doppler ultrasound to identify the intraabdominal portion of the umbilical arteries as a screening and diagnostic technique for single umbilical artery. (See "Single umbilical artery".)
Although this expanded assessment is not the standard of care in most ultrasound departments, the author believes it is useful because a higher risk for adverse perinatal outcome has been associated with specific characteristics of the umbilical cord, such as thinness [13] and abnormal coiling [14]. Other cord abnormalities, such as cysts and masses, may be noted incidentally during the expanded examination and also may have an adverse effect on pregnancy outcome, as discussed in the sections below.
First-trimester examination — The umbilical cord can be visualized sonographically from the eighth gestational week. In the first trimester, the cord is usually coiled and approximately the same length as the crown-rump length (image 2) [15].
Determining the number of vessels is difficult to establish by direct examination in the first trimester, even with color flow imaging. However, in the late first trimester, it is almost always possible to at least visualize the paravesical umbilical vessels with color Doppler ultrasound in the axial view of the fetal pelvis.
Before the 12th gestational week, the fetal insertion often appears bulky due to normal physiological midgut herniation of intestinal loops into the cord [16]. Herniation after 11 weeks of gestation is not normal and suggests an anterior abdominal wall defect. (See "Gastroschisis" and "Omphalocele: Prenatal diagnosis and pregnancy management".)
The placental insertion site can be easily identified, especially if color flow imaging is used, enabling diagnosis of marginal and velamentous insertion in early pregnancy [17]. (See "Velamentous umbilical cord insertion and vasa previa".)
VASCULAR ABNORMALITIES
Single umbilical artery — Single umbilical artery (SUA) refers to a variation of umbilical cord anatomy in which there is only one umbilical artery, rather than the normal two umbilical arteries.
Prenatal diagnosis, clinical significance, and management — Prenatal diagnosis of SUA is based on the finding of a two-vessel cord on transverse and longitudinal views of a free loop of cord (image 3). Visualization of one artery going around the fetal bladder instead of one artery on each side of the bladder supports the diagnosis (image 4).
SUA may be an isolated finding or associated with aneuploidy or other congenital anomalies. Prenatal diagnosis, clinical significance, and pregnancy management are reviewed in detail separately. (See "Single umbilical artery".)
Hypoplasia of one umbilical artery — Hypoplasia of one umbilical artery is a variant of SUA in which both arteries are present but with a gross disparity in their size. The hypoplastic but functional artery can occasionally be detected prenatally by ultrasound [18-24].
Prenatal diagnosis — The prenatal diagnosis of a hypoplastic umbilical artery is based on identification of all of the following [18]:
●Two patent umbilical arteries
●One artery that is smaller than the other (at least 50 percent smaller)
●Discordant umbilical artery flow velocity waveforms between the arteries
Size discordancy is best appreciated in a magnified cross-sectional view of the umbilical cord [19]. There is no universal standard definition of discordancy; differences in arterial diameter of 1 to 3 mm between arteries have been described and occur in up to 2 percent of pregnancies [18,21,22]. The prevalence of discordancy is much lower if it is defined as >50 percent difference between arterial diameters. Using this definition, only 12 cases of hypoplastic umbilical artery were identified among 31,000 consecutive second- and third-trimester ultrasound scans [20]. The low prevalence (0.04 percent) in this series was probably the result of using the very strict definition of hypoplastic umbilical artery and the inclusion of many early second-trimester pregnancies. The detection of marked discordancy between umbilical arteries is difficult to document before 20 weeks due to the small size of the arteries early in gestation.
Color Doppler ultrasound is used to confirm flow within the hypoplastic artery (image 5), since absence of flow suggests an atrophic nonfunctional artery. Doppler is also used to document arterial flow velocity waveforms, which are discordant when one artery is hypoplastic [18,19]. The resistance index is almost always higher in the smaller artery, and there may be absent end-diastolic flow.
Clinical significance — The clinical significance of hypoplastic umbilical artery has not been clearly established. An increased risk of adverse pregnancy outcome has been reported, as well as associations with maternal diabetes mellitus, polyhydramnios, fetal growth restriction, congenital anomalies, abnormal insertion of the umbilical cord, and placental abnormalities [18-23]. Among 39 prenatally diagnosed cases of hypoplastic umbilical artery, seven fetuses (18 percent) had associated anomalies, including three cases of trisomy 18 and one case each of biliary atresia, hydronephrosis and duplex collecting system, agenesis of the corpus callosum and kyphoscoliosis, and tetralogy of Fallot [18-23]. The high prevalence of associated structural anomalies in these reports should be interpreted with caution because most cases of hypoplastic umbilical artery were diagnosed in a high-risk population.
Management — A thorough examination of fetal anatomy and both cord insertion sites should be performed to look for additional abnormalities. The author suggests ultrasound examination for fetal growth and assessment of amniotic fluid at 28 and 34 weeks. This approach is based on the limited clinical experience obtained from the few case reports and small series reported in the literature.
At any follow-up ultrasound examination, he suggests measuring Doppler flow in both umbilical arteries. Clinical management is based on the Doppler findings of the normal diameter artery.
Postnatal confirmation — Constriction of the umbilical arteries after birth makes the diagnosis difficult to document by visual examination postnatally. However, when histologic examination is indicated, histologic examination of a cross-section of the umbilical cord can document the diagnosis.
Supernumerary vessels — The most common type of multivessel cord contains two veins and two arteries. The extra vein has been attributed to persistence of the extracorporeal portion of the right umbilical vein [25], but could also represent abnormal splitting of an umbilical vessel in the third to fifth week of embryo development.
Prenatal diagnosis — Prenatal diagnosis is based on visualization of more than three blood vessels in the umbilical cord (image 6).
Misdiagnosis of a multivessel cord can occur when the transverse view of the cord is through a false knot and includes loops of the same vessel. This also accounts for some four-vessel cords in histologic sections.
Clinical significance — The clinical significance of supernumerary vessels has not been clearly established. More than three vessels in the umbilical cord is most common in conjoined twins and is an ultrasound landmark for diagnosis of thoracopagus and omphalopagus twins, which share the same cord [26,27]. In the prenatally detected cases in singletons, a four-vessel cord has been associated with holoprosencephaly and polyhydramnios in one case, an omphalocele in two cases, triploidy in one case, and was an isolated finding in a normal fetus in another 12 cases [6,25,28-30].
A four-vessel cord has been noted in normal neonates [31-33], but also in neonates with multiple and different congenital anomalies (eg, trisomy 18, heterotaxy syndrome, hypertrophic cardiomyopathy, anterior chest wall defect plus bilateral cleft lip and palate) [29]. In one case, four vessels (2 arteries, 2 veins) were found in the cord of a macerated stillborn with multiple anomalies, including ectopia cordis, bifid liver, and bilateral cleft lip and palate [34].
Management — If a multivessel cord is identified, a thorough examination of fetal anatomy should be performed to look for associated anomalies and to exclude conjoined twins in twin pregnancies. (See "Twin pregnancy: Overview", section on 'Fetal complications'.)
Aneurysm and varix — Aneurysm and varix are focal dilations of the umbilical artery and vein, respectively. Both are rare.
Prenatal diagnosis — The diagnosis of aneurysm or varix should be suspected when focal dilation is observed in any of the umbilical vessels. Umbilical vein varix typically occurs in the intraabdominal portion of the vein but can occur in the intraamniotic portion as well (picture 1) [35-39]. There are two criteria for diagnosis of intraabdominal umbilical vein varix: diameter greater than 9 mm or 1.5 times larger (diameter greater than 50 percent) of the nondilated portion of the intraabdominal umbilical vein [40,41].
Color Doppler (image 7) and color flow imaging are useful in distinguishing an aneurysm from a varix by demonstrating whether there is pulsatile, nonpulsatile, or turbulent flow within the mass. With an aneurysm, the feeding vessel is arterial, and therefore, pulsatile flow is obtained when spectral analysis is applied to the vascular mass. With a varix, the incoming vessel is venous, and the flow within the vascular mass is nonpulsatile or turbulent.
Differential diagnosis includes all types of cystic masses of the cord, including pseudocyst or true cyst. However, color Doppler ultrasound can easily differentiate a cystic from a vascular mass by determining absence or presence of blood flow signal within the mass, respectively.
Clinical significance — Aneurysm and varix have been associated with fetal demise [42-48]. Varix of the intraamniotic segment of the umbilical vein can rupture, resulting in intraamniotic hemorrhage through the amniotic sheath, with fetal exsanguination leading to fetal death [49]. Variceal thrombosis can also occur [49,50]. A meta-analysis of intraabdominal umbilical vein varix reported the following pooled proportions for prevalence: additional ultrasound anomalies in 19 percent, small for gestational age (SGA) in 3.9 percent, chromosomal anomalies in 4.6 percent (trisomy 21 in three cases, 22q deletion in two cases, one case each of unspecified other anomalies), and fetal demise in 1.3 percent [51]. Of note, isolated intraabdominal umbilical vein varix was not associated with any cases of chromosomal abnormality or demise, but SGA occurred in 3.7 percent of these cases. In fetuses with nonisolated varix, chromosomal anomalies occurred in 19.6 percent, fetal demise in 7.3 percent, and SGA in 5.3 percent.
There is minimal information on the long-term outcome of children diagnosed with varix prenatally [52]. In the only available study, a possible association with neurodevelopmental delay was noted [52]; however, methodological issues limit the validity of this finding [53].
A few cases of umbilical artery aneurysm have been reported prenatally in association with SUA, other congenital anomalies, trisomy 18 (picture 2), and fetal demise [44,54-60].
Management — Given the rarity of these lesions, the natural history and optimum management of affected pregnancies are unknown. Frequent fetal surveillance with nonstress testing, ultrasound surveillance, and delivery when fetal lung maturity is likely has been suggested because of reports of fetal demise [44,61]. Fetuses with isolated intraabdominal umbilical vein varix without growth restriction appear to be at low risk but probably should still be followed closely, with early delivery if abnormalities (eg, presence of thrombus, signs of fetal impairment) are noted.
CYSTIC ABNORMALITIES — Cystic abnormalities of the umbilical cord (picture 3) may be true cysts or pseudocysts; a definitive diagnosis can only be made by histologic examination (pseudocysts lack an epithelial lining). On ultrasound, both true cysts and pseudocysts appear as a fluid-filled mass in close proximity to the umbilical cord.
Management depends on the type, size, and location of the cyst; gestational age at detection; associated anomalies; and potential for complications, such as compression of surrounding vessels or torsion along the axis of the cord.
First-trimester cysts — Umbilical cord cysts have been identified in 2 to 3 percent of pregnancies scanned at 7 to 14 weeks of gestation [62,63].
The origin of first-trimester umbilical cord cysts is unknown. One theory is that they represent embryonic remnants such as an allantoic or omphalomesenteric cyst, amniotic inclusion cyst, or mucoid degeneration or edema of the Wharton's jelly (pseudocysts). In the only case in which sonographic-histopathologic correlation is available, an amniotic inclusion cyst and adjacent mucoid degeneration of Wharton's jelly were found, suggesting first-trimester umbilical cord cysts could represent either entity [64].
The rapid resolution of first-trimester cysts suggests they are pseudocysts rather than true cysts. They are always located lateral to the umbilical vessels, which further suggests that they are pseudocysts rather than a cystic component of embryologic remnants. Since the formation of these cysts is coincidental with both the onset of umbilical cord coiling and formation of the physiologic midgut hernia, these developmental phenomena could increase hydrostatic pressure within the umbilical vessels, favoring exudation of water into Wharton's jelly and formation of pseudocysts [62].
Prenatal diagnosis — Prenatal diagnosis is based on observation of a round, thin-walled anechoic structure in the amniotic cavity in close approximation to the umbilical cord and separate from the fetal pole and physiologic hernia. The cyst must be clearly differentiable from the yolk sac, which has a more echoic wall and is extra-amniotic (image 8). Color Doppler imaging is useful to exclude the possibility of a prominent umbilical vessel or an aneurysm and to document the cyst's relationship with the umbilical vessels (lateral to or surrounded by the umbilical vessels).
The combination of an umbilical cord cyst and megacystis at the 11- to 14-week ultrasound scan suggests a patent urachus [65].
Clinical significance — Single cysts that present at 8 to 9 weeks of gestation usually disappear by the second trimester and are associated with normal pregnancy outcome [66,67]. In contrast, multiple cysts detected in the late first trimester (ie, 11 to 14 weeks) are more likely to be associated with structural anomalies and aneuploidy. In one study, fetal structural anomalies and chromosomal abnormalities were identified in approximately 25 percent of cases in a high-risk population [62]. In a report of 24 cases of umbilical cord cysts detected between 7 to 14 weeks, all 18 fetuses presenting with a single cyst had complete resolution and normal pregnancy outcome, whereas five of the six fetuses presenting with multiple cysts had poor outcome, including four miscarriages and one case of obstructive uropathy [63].
Management — Expectant management is appropriate since most cysts resolve and are not predictive of adverse pregnancy outcome. Cysts that persist are managed as true or pseudocysts. (See 'Second- and third-trimester true cysts' below and 'Second- and third-trimester pseudocysts' below.)
As most of the early cysts resolve by the time of a nuchal translucency scan at 11 to 13 weeks, patients with normal ultrasonographic findings at that time can be reassured regarding a normal pregnancy outcome with respect to this finding, and subsequent prenatal care can be routine. If early cysts persist at the time of a nuchal translucency scan at 11 to 13 weeks, the author suggests detailed evaluation of fetal anatomy for abnormalities in the second trimester.
Second- and third-trimester pseudocysts — Umbilical cord pseudocysts are more common than true umbilical cord cysts. The pathogenesis is unknown. One theory is that they represent an area of focal edema. In these cases, increased vascular pressure within the umbilical-placental circulation increases umbilical cord hydrostatic pressure, which favors transfer of fluid into Wharton's jelly [68]. Increased vascular pressure may be caused by an abdominal wall defect or by obliteration of portions of the villus vasculature, as seen with fetal growth restriction.
Pseudocysts could also result from focal cystic or mucoid degeneration of Wharton's jelly due to a local pathological process of the umbilical cord [69]. When associated with angiomyxoma of the cord (see 'Angiomyxoma' below), exudation of plasma from the tumor may be an etiologic factor in cyst formation.
Prenatal diagnosis — The ultrasound appearance of umbilical cord pseudocyst varies widely. The most common feature is a large, round, cystic lesion located either close to the fetal insertion site or in a free loop of cord (image 9). Occasionally, more than one cystic mass is detected, usually close to each other; multiple small cysts may be detected in close relation to a localized thickening of Wharton's jelly. When associated with an umbilical cord angiomyxoma, the pseudocyst is always located close to the tumor and may be large.
Clinical significance — If the pseudocyst appears to be an isolated finding, the risk of adverse pregnancy outcome is probably not increased, although few such cases have been reported [70]. There is a potential risk for rare local complications such as torsion or thrombohematoma, which could lead to fetal death [71,72].
Nonisolated pseudocysts of the umbilical cord have been associated with both fetal chromosome abnormalities and with fetal structural anomalies, particularly omphalocele [68,73-75]. In one review of 13 prenatally diagnosed umbilical cord cystic lesions histologically proven to be pseudocyst, eight were associated with aneuploidy and two were euploid with other anomalies [75]. In the largest series of umbilical cord pseudocysts in a high-risk population, chromosome abnormalities were noted in seven of 13 cases, and three additional euploid fetuses had structural defects, including one each of cystic hygroma, omphalocele, and acrania [68].
Management — The prenatal detection of a pseudocyst in the umbilical cord should prompt a detailed examination of the fetal anatomy, including markers of aneuploidy (see "Sonographic findings associated with fetal aneuploidy"). If additional abnormalities or findings suggestive of aneuploidy are noted, patients are offered fetal chromosome analysis (see "Prenatal genetic evaluation of the fetus with anomalies or soft markers"). In the absence of additional anomalies or aneuploidy, the author evaluates fetal growth at 28, 32, and 36 weeks of gestation.
At each ultrasound evaluation, the size of the pseudocyst(s) should be monitored. Cysts >3 cm can lead to twisting or thrombosis of the cord. Rapid growth of the cyst can result in compression of the neighboring vessels.
Aspiration of the cyst is indicated if it is very large and causing symptoms. In a patient with preterm contractions, the author managed a large pseudocyst associated with an angiomyxoma (image 10) with two percutaneous sonographically-guided aspirations of 400 mL of fluid at 27 and 32 weeks. The cyst fluid reaccumulated so a cesarean birth was performed at term due to presumed fetal dystocia. Postpartum examination revealed a short cord, a large pseudocyst, and an angiomyxoma of the cord.
Second- and third-trimester true cysts — True umbilical cord cysts originate from embryonic remnants [76,77].
●Allantoic cysts originate from persistence of the urachus [78]. A patent urachus may allow extravasation of urine from the bladder into the base of the cord, resulting in cystic dilation of the extraembryonic portion of the allantois. Less frequently, the urine may leak into Wharton's jelly, resulting in a giant umbilical cord [79-83].
●Omphalomesenteric cysts originate from persistence of the vitelline duct [84].
Prenatal diagnosis — Prenatal diagnosis of allantoic cysts has been reported several times, usually in association with urachal anomalies [78,85-90], whereas prenatal diagnosis of omphalomesenteric cysts has only been reported twice and without conclusive histologic confirmation [91,92].
Communication between the cyst and the fetal bladder is a key feature of an allantoic cyst due to patent urachus (image 11). However, this communication is not always present and only rarely detected prenatally. Embryologically, the allantois is the only vestigial remnant located at the center of the umbilical cord and is surrounded by the umbilical vessels. If an allantoic cyst develops because of retrograde micturition into the umbilical cord, the umbilical vessels separate and surround the cyst (figure 3), which can be seen with color Doppler (picture 4) [88,89]. By comparison, the vessels remain together and on only one side of the cyst wall with other types of cysts because the cyst will displace the vessels.
An allantoic cyst is always in close relationship with the fetal anterior abdominal wall; thus, it can be mistaken for an anterior abdominal wall defect. Careful examination of the umbilical cord insertion in the fetal abdomen establishes the correct diagnosis, which may include both an allantoic cyst and an omphalocele [93].
Clinical significance — A rapidly enlarging cyst has been reported to produce progressive obliteration of the blood flow within the cord, necessitating urgent delivery for a nonreactive fetal heart rate tracing with bradycardia and late decelerations [94]. Prenatal resolution of allantoic cysts has also been reported [86]. This does not necessarily mean that the urachus became obliterated; resolution has also been attributed to cyst rupture [95].
All allantoic cysts are associated with urachal anomalies, so patients should be counseled that the neonate might leak urine through the umbilicus and require surgery. Obstructive uropathy has also been reported [62,95-97]. For these reasons, pediatric urology consultation is recommended.
Management — The author performs weekly follow-up examinations to monitor the growth of the cyst until the size stabilizes. He performs color Doppler velocimetry of the umbilical artery during these examinations to determine whether blood flow is impeded by compression from the cyst.
SOLID OR COMPLEX ABNORMALITIES — Solid or complex masses of the umbilical cord include true tumors (eg, angiomyxomas and teratomas) and pseudotumors/hematomas. Umbilical cord hematomas are sometimes termed pseudotumors because they have a similar appearance to true tumors on prenatal ultrasound, but flow should never been seen internally within a hematoma, whereas it may be seen within a tumor [98].
Abdominal wall defects such as omphaloceles, gastroschisis, and umbilical hernias can also present prenatally as echogenic masses in the base of the cord; however, they are not considered abnormalities of the umbilical cord, but rather gastrointestinal or abdominal wall malformations. Nevertheless, these conditions must be considered in the differential diagnosis.
Angiomyxoma — Angiomyxomas are extremely rare and arise from proliferation of the primitive angiogenic mesenchyme of the cord [76,77]. The term angiomyxoma is based on the prominent myxoid material contained within the tumor [99].
Prenatal diagnosis — Because of its rarity, the prenatal diagnosis of angiomyxoma is based on findings described in isolated case reports [100-102]. The tumor usually presents as a hyperechogenic mass in close relation to the umbilical vessels and is frequently associated with a pseudocyst of variable size. Sometimes the cyst is the most prominent finding [102,103], with one case reporting a 16 cm cyst that required prenatal aspiration to allow vaginal birth [103]. Color Doppler ultrasound can support the suspected diagnosis by demonstrating blood vessels with low flow within the echogenic component of the tumor (image 12).
Angiomyxomas can mimic small omphaloceles, especially those located close to the fetal insertion of the umbilical cord [104].
Clinical significance — Although angiomyxomas may be considered a counterpart of chorioangioma of the placenta, which is sometimes associated with pregnancy complications if large, most cord angiomyxomas are incidental findings of no clinical significance. However, compression of the adjacent umbilical vessels, fetal hydrops, and torsion around the axis of the cord can occur and lead to fetal death.
Neonates with angiomyxoma of the cord may also demonstrate skin hemangiomas [105].
Management — Tumor growth could cause umbilical vessel compression; therefore, the author serially monitors tumor growth and Doppler flow in the umbilical vessels. The frequency depends on the size and growth rate of the tumor. In the third trimester, he also performs nonstress testing. In case of abnormal Doppler waveforms in the umbilical vessels, percutaneous aspiration of the cyst or prompt delivery should be considered; this decision depends on the gestational age.
Teratoma — Teratomas of the cord are rare tumors derived from ectopically located totipotential germ cells and containing tissue from the three germ-cell layers [76,77]. Some investigators have proposed that cord teratomas represent small acardiac twins rather than true neoplasms [106-108].
Prenatal diagnosis — Teratoma of the cord should be considered whenever a heterogeneous lesion of the cord is detected. Prenatal diagnosis has been reported only twice [109,110].
Differential diagnosis mainly includes small acardiac twins, especially those of the amorphous type. Acardiac twins can be differentiated from umbilical cord teratomas by the following criteria: Acardiac twins always have an independent, although rudimentary, umbilical cord, whereas teratomas are located within the umbilical cord; they usually have a craniocaudal skeletal organization, whereas teratomas do not; and they are always covered by skin, whereas teratomas are covered by amnion. (See "Twin reversed arterial perfusion (TRAP) sequence".)
Placental teratomas should also be excluded. Findings that support the diagnosis of placental teratoma rather than cord teratoma include a location closely related to the placenta or a tumor surrounded by placental tissue [111].
The possibility of an umbilical cord hernia should also be considered [112]; however, a definitive histopathological examination is usually needed to establish the definitive diagnosis. (See "Omphalocele: Prenatal diagnosis and pregnancy management", section on 'Differential diagnosis'.)
Clinical significance — In the two cases detected prenatally, one was associated with an omphalocele and the other was associated with trisomy 13. Both pregnancies diagnosed with cord teratomas prenatally were terminated because of associated abnormalities [109,110], so no information on the natural history of affected pregnancies is available.
A review of postnatally diagnosed cases revealed that four of the 10 fetuses/newborns died due to associated malformations [109]. In fetuses with no associated anomalies, the prognosis appears to be good.
Management — Tumor growth could cause umbilical vessel compression; therefore, the author serially monitors tumor growth and Doppler flow in umbilical vessels. The frequency depends on the size and growth rate of the tumor.
Hematoma — Spontaneous cord hematomas are rare. Iatrogenic cord hematomas following an invasive procedure are more common, especially after percutaneous umbilical blood sampling or transfusion [113].
Prenatal diagnosis — Umbilical cord hematomas are sometimes called pseudotumors because they have a similar appearance to true tumors on prenatal ultrasound [98]. Hematomas may appear as solid masses of variable shape and size in close relation to the umbilical cord or have a variable appearance, depending on the time elapsed between the bleeding and sonographic evaluation. Acute hematomas appear isoechoic or may be heterogeneous, while chronic hematomas appear hypoechoic to anechoic.
Clinical significance — Cord hematomas may cause discordant umbilical artery flow velocity waveforms due to uneven compression of the arteries [114]. Intraamniotic clots secondary to placental abruption can attach to the umbilical cord and can resemble a spontaneously generated umbilical cord hematoma [115].
Fetal bradycardia is often observed as an iatrogenic cord hematoma and/or hemorrhage develop during postprocedure monitoring.
Management — Management of an acute hematoma that develops during an invasive procedure is described separately. (See "Fetal blood sampling", section on 'Cord hematoma'.)
The author suggests follow-up sonographic examination to assess the size and appearance of the hematoma and to obtain blood flow velocity waveforms of the umbilical arteries. Spontaneous hematomas are usually self-limited and do not require long-term assessment.
CORD INSERTION SITE ABNORMALITIES — Cord insertion at the fetal and placental sites is evaluated to determine whether it is normal (image 13) or abnormal [116-118]. (See "Gross examination of the placenta", section on 'Placental insertion site'.)
Placental site abnormality — Both marginal and velamentous insertions are more common in multiple gestations and in pregnancies achieved with the use of reproductive techniques.
●Velamentous insertion – Velamentous insertion (image 14) refers to the placental end of the cord consisting of divergent umbilical vessels surrounded only by fetal membranes with no Wharton's jelly. The membranous vessels are at risk for rupture, kinking, and compression, which increase the risk for adverse pregnancy outcome [119,120]. The prevalence was 1.4 percent among singleton pregnancies in a systematic review [120]. Diagnosis, clinical significance, and management are discussed in more detail separately. (See "Velamentous umbilical cord insertion and vasa previa", section on 'Velamentous umbilical cord insertion'.)
●Marginal insertion – Marginal insertion refers to an otherwise normal umbilical cord inserting at the edge of the placenta. It has been associated with a variably increased risk of adverse pregnancy outcome, but risks are generally less compared with velamentous insertion [121]. The prevalence was 6.15 percent in a systematic review [121]. (See "Gross examination of the placenta", section on 'Placental insertion site'.)
•The diagnosis is established when the placental insertion site is located within 1 to 2 cm from the placental edge; available data are inadequate for determining the optimum precise threshold. This can easily be determined by prenatal ultrasound by the simultaneous visualization of the umbilical cord insertion site and the margin of the placenta [122].
•There are conflicting reports regarding the clinical significance of marginal insertion detected prenatally. In a study that subclassified marginal insertions into those located within 1 cm, between 1 and 2 cm, and between 2 and 3 cm, only those inserted within 1 cm were mildly associated with abnormal perinatal outcome [123]. Therefore, it seems reasonable to reassure patients with a marginally inserted cord and avoid follow-up scans based solely on this finding.
Fetal site abnormality
●Omphalocele – Omphalocele is a midline abdominal wall defect of variable size, covered by a membrane of amnion and peritoneum with Wharton's jelly between the two layers, and containing abdominal contents. The defect occurs at the base of the umbilical cord, with the cord/umbilical vessels inserting at the apex of the omphalocele sac. Diagnosis, clinical significance, and management are discussed in more detail separately. (See "Omphalocele: Prenatal diagnosis and pregnancy management".)
●Other – Other fetal cord insertion site abnormalities are rare and include bladder exstrophy, cloacal malformation, and amniotic bands. (See "Body stalk anomaly and cloacal exstrophy: Prenatal diagnosis and management" and "Amniotic band sequence".)
●Gastroschisis – Gastroschisis consists of a relatively small (<4 cm) paraumbilical abdominal wall defect, usually to the right of the midline, with visceral herniation (image 15). The umbilical cord insertion site is normal but mentioned here because it is adjacent to and separate from the defect. Diagnosis, clinical significance, and management are discussed in more detail separately. (See "Gastroschisis".)
ABNORMAL CORD TWIST OR COIL — The umbilical cord has a characteristic twist or coil (figure 4). Few investigators have studied cord twist antenatally, and data from these studies are inconsistent [124-128]. This is because sonographic measurement of the number of complete coils per centimeter of cord is technically difficult, the degree of coiling along the cord varies, and no prenatal gestational age-specific standard exists for defining hypocoiled and hypercoiled cords [12].
Prenatal diagnosis — Three umbilical cord coiling patterns are easily identified by examining a longitudinal view of a free loop of the umbilical cord [12].
●In type I, the umbilical vein and arteries course together in a straight line parallel to each other.
●In type II, the umbilical arteries coil around the vein, which is predominantly straight or undulating.
●In type III, the vein and arteries course together in a helical fashion. Type III umbilical cords in which the loops are in close apposition to the previous and following loops are considered hypercoiled; hypercoiling has been associated with abnormal pregnancy outcome [129].
Clinical significance — Studies of postnatal examination of the umbilical cord have clearly shown an association between hypocoiled and hypercoiled cords and adverse perinatal outcomes, including fetal death. (See "Gross examination of the placenta", section on 'Coiling'.)
Management — The author monitors pregnancies with either hypo- or hypercoiled umbilical cords closely, especially in the third trimester. He performs serial ultrasound examinations, including Doppler studies and biophysical profile scoring, serial nonstress tests, and asks the patient to perform fetal movement counts.
THIN CORD — A thin cord is the result of a deficiency of Wharton's jelly.
Prenatal diagnosis — When a thin cord is suspected, some authors have recommended imaging a midsegment of the umbilical cord in cross-section, measuring the cross-sectional area using the software programmed into the ultrasound machine, and then comparing the measurement with an established umbilical cord area nomogram [130]. However, this is not part of the standard or specialized ultrasound examination.
Clinical significance — The vessels in a thin cord are more vulnerable to compression, which may explain the association between thin umbilical cords and fetal growth restriction and abnormal intrapartum fetal heart rate tracings [13].
Management — The author monitors pregnancies with thin umbilical cords closely, especially in the third trimester. He performs serial ultrasound examinations, including Doppler studies and biophysical profile scoring, and assessment of fetal growth and amniotic fluid volume. He also orders serial nonstress tests and has the patient perform fetal movement counts.
KNOTS
True knot
Prenatal diagnosis — Prenatal identification of a true knot is rare and challenging [131-134]. The ultrasonographic appearance has been described as similar to a four-leaf clover, but this pattern is nonspecific and can be seen with false knots or closely apposed loops of umbilical cord [133].
Another characteristic sonographic sign is the "hanging noose," which is a cross-sectional view of the cord closely surrounded by a loop of the cord (image 16).
Use of color Doppler ultrasound, particularly three-dimensional power Doppler imaging (image 17) [135], may support the suspected diagnosis.
Clinical significance — True knots occur in <1 percent of births and are generally single and loose (picture 5A-B) [136,137]. Loose knots are unlikely to be clinically significant. Tight (picture 6) or multiple true knots and knots associated with coiling or twisting of the cord increase the risk of fetal demise, particularly if the cord is long and during the second trimester when the fetus has a lot of room to move. In a systematic review, the likelihood of stillbirth was more than fourfold higher in pregnancies with a true cord knot (odds ratio 4.65, 95% CI 2.09-10.37) [138]. (See "Gross examination of the placenta", section on 'Knots'.)
Management — The author monitors pregnancies with an umbilical cord knot closely, especially in the third trimester. He performs serial ultrasound examinations, including Doppler studies and biophysical profile scoring, and assessment of fetal growth and amniotic fluid volume. He also orders serial nonstress tests and has the patient perform fetal movement counts.
False knot — False knots are tortuosities of the umbilical vessels that form bulges (picture 7) [139,140]. They are not associated with adverse fetal outcome so prenatal care is routine. (See "Gross examination of the placenta", section on 'Knots'.)
OTHER — Prenatal diagnosis and management of other umbilical cord abnormalities are discussed separately.
Nuchal cord — (See "Nuchal cord".)
Funic presentation and prolapse — (See "Umbilical cord prolapse".)
Absent umbilical cord — (See "Body stalk anomaly and cloacal exstrophy: Prenatal diagnosis and management".)
SUMMARY AND RECOMMENDATIONS
●Normal cord – The umbilical cord contains two arteries and one vein surrounded by a gelatinous stroma (ie, Wharton's jelly) and covered by a single layer of amnion. (See 'Normal umbilical cord anatomy' above.)
●Imaging the cord – Basic goals of umbilical cord imaging are to determine the number of vessels and assess the fetal and placental insertion sites. The two arteries and vein can be seen clearly in both the transverse and longitudinal planes using conventional two-dimensional imaging techniques (image 1). Color Doppler improves visualization. (See 'Ultrasound examination of the umbilical cord' above.)
●Umbilical cord abnormalities – Abnormalities of the umbilical cord can be vascular, insertional, cystic, solid or complex, or may involve knotting, twisting, thinning, or position. (See 'Vascular abnormalities' above and 'Cystic abnormalities' above and 'Solid or complex abnormalities' above and 'Cord insertion site abnormalities' above and 'Abnormal cord twist or coil' above and 'Thin cord' above and 'Knots' above and 'Other' above.)
●Clinical significance and management – The potential clinical significance of a cord abnormality and management of affected pregnancies depends on the specific abnormality. (See 'Vascular abnormalities' above and 'Cystic abnormalities' above and 'Solid or complex abnormalities' above and 'Cord insertion site abnormalities' above and 'Abnormal cord twist or coil' above and 'Thin cord' above and 'Knots' above and 'Other' above.)
ACKNOWLEDGMENT — The UpToDate editorial staff acknowledges Neil J Sebire, FRCP, who contributed to an earlier version of this topic review.
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