Vessel Abnormalities in the Fetal Umbilical Cord

Question

Kindly let me know the significance of the ultrasound (color Doppler) scan showing only 1 umbilical artery and 2 veins with no other features of congenital anomalies for a 22-week-old IVF gestation.

Dr. Jai Thilak, MBBS, MS, MCh

Response From the Experts

Umbilical cord abnormalities can be detected ultrasonographically and may be associated with fetal anomalies, chromosome abnormalities, and potential complications during pregnancy.

The normal umbilical cord contains 2 arteries and 1 vein. The umbilical vein carries oxygenated blood from the placenta to the left portal vein in the fetal liver. The 2 umbilical arteries are continuous with the internal iliac arteries and carry deoxygenated blood from the fetus to the placenta.

The most common abnormality of the umbilical cord is a single umbilical artery (SUA), which occurs in 0.5% to 2.5% of pregnancies.^[1] This finding is sometimes referred to as a 2-vessel cord. The loss of 1 umbilical artery likely occurs secondary to thrombotic atrophy of a previously normal artery. Less likely, the loss may result from primary agenesis of the artery.^[2] It is the left umbilical artery that is more commonly absent. The clinical significance of an SUA is not completely understood, and there are many different reports regarding outcomes of fetuses with this finding.

An SUA should be confirmed at the fetal end of the cord. A normal variant can occur in which both umbilical arteries fuse before entry into the placenta. Because the cord is usually coiled, leading to a variety of appearances, one must rely on a true transverse axial section of the umbilical cord to ascertain the correct number of vessels. In addition, the umbilical arteries can be identified as they run along the margin of the bladder using color Doppler ultrasonography in an oblique plane through the lower end of the fetal abdomen.^[2]

SUAs have been reported to increase incidence of fetal anomalies by 30% to 60%.^[2] SUA has been associated with anomalies in all major organ systems (eg, the cardiovascular, gastrointestinal, and central nervous systems). The most common congenital abnormality usually involves the kidneys.^[2] In more than half of the cases with a renal basis, the clinical significance is minor. In addition, SUA is associated with an increased risk of such chromosome abnormalities as trisomy 13, trisomy 18, and triploidy.^[1]

Data also suggest that the finding of SUA is associated with an increased incidence of intrauterine growth restriction (IUGR).^[3] In addition, some reports indicate a higher incidence of preterm delivery and stillbirth.^[3] This finding may be related to the association of SUA with chromosomal abnormalities and anomalies of the major organ systems.

An umbilical cord with more than 2 arteries or more than 1 vein is called a multivessel cord. A multivessel cord is rare and has been reported in conjoined twins.^[2] Abnormalities of the umbilical vein are rare. Normally, the right umbilical vein atrophies at 6 weeks' gestation, leaving a single left umbilical vein. Persistence of the right umbilical vein occurs in approximately 1 in 400 pregnancies.^[1] This finding is usually identified ultrasonographically in the fetus, but not specifically in the umbilical cord, and can be associated with many congenital malformations.

When the diagnosis of SUA is made on antenatal ultrasound, a detailed anatomic survey should be performed. A fetal echocardiogram should be considered. Genetic counseling should also be considered. If no other anomalies are revealed on ultrasound, an amniocentesis for chromosome evaluation is not absolutely indicated. Finally, a repeat ultrasound in the third trimester to evaluate fetal growth may be appropriate, as well as close antenatal monitoring because of the associated risks of IUGR, preterm birth, and stillbirth.

Medscape Ob/Gyn. 2003;8(1) © 2003  Medscape

Cite this: Peter S Bernstein, Peter Van Eerden. Vessel Abnormalities in the Fetal Umbilical Cord - Medscape - May 15, 2003.