Abnormalities of the intra-abdominal fetal umbilical vein: reports of four cases and a review of the literature.

Anomalies of the fetal umbilical vessels are rare, excepting single umbilical arteries which occur in 0.2-1.0% of pregnancies. Abnormalities of the intra-abdominal umbilical vein may be categorized into three main groups: (1) the ductus venosus is patient but the right umbilical vein persists; (2) the ductus venosus is not patent, and there is extrahepatic continuation of the umbilical vein; and (3) the umbilical vein takes a normal course but is abnormally dilated. We describe cases of each of these types of anomaly, including the first report of prenatal diagnosis of insertion of the umbilical vein into the iliac vein, and review the literature on this subject.