Morphological assessment of the umbilical cord with three-dimensional ultrasonography

The long cylindrical cord covered by a layer of amnion that extends from the umbilicus of the fetus to the fetal surface of the placenta is known as the umbilical cord, or, in older medical textbooks, as funiculis umbilicalis. The two umbilical arteries extend as branches of the internal iliac arteries that emerge from the fetal body at the umbilicus, and run a helical course through the umbilical cord carrying venous blood to the placenta. In most normal placentas, the umbilical arteries anastomose within 2 cm of insertion into the placenta. The fetal umbilical vein emerges from the placenta and carries oxygenated blood to the fetus. The cord vessels are supported by a matrix of myxomatous connective tissue known as Wharton's jelly. The average length of the umbilical cord is approximately 55 cm at term, but extreme variations in length can occur for unknown reasons. The normal umbilical cord is spiralled. On rare occasions, remnants of the omphalomesenteric and allantoic ducts may be found in the term cord. True knots, false knots, cysts, tumors and vascular abnormalities occur occasionally. Early detection is desirable because some of these abnormalities may affect the fetus adversely, and others are associated with fetal malformations and chromosomal anomalies. Complementary use of Doppler scanning two-dimensional ultrasonography and three-dimensional ultrasonography allows the prenatal diagnosis of most cord abnormalities.