A normal umbilical cord, which connects the fetus to the placenta, has two arteries and one vein. The vein carries oxygenated blood and nutrients from the mother to the fetus, and the arteries take waste from the fetus to the mother for it to be expelled from the body. The three vessels within a normal umbilical cord are separated and cushioned by Wharton's jelly, which is a spongy tissue. Doctors often use ultrasound technology to detect umbilical cord complications during pregnancy. An abnormal cord might be overly long, too short or missing an artery, to name some of the most common complications.
The typical umbilical cord forms about five weeks after conception and grows until about 28 weeks' gestation, at which point it should be 22-24 inches (55.9-61 cm) in length. The diameter of a normal umbilical cord is usually about 0.4-0.8 inches (1-2 cm). A cord that is abnormally short, such as 12 inches (30.5 cm) or less, might result in a small baby or fetal distress during delivery, and it can indicate a genetic issue. An umbilical cord that measures more than 27 inches (68.6 cm) can result in entanglement in the womb and might signal that the fetus is hyperactive, because the cord tends to stretch as the baby moves.
Another common aspect of a normal umbilical cord is the presence of three vessels, with one being the vein that brings nutrients and blood to the fetus. The other two vessels are arteries, which take waste away from the fetus after the oxygenated blood circulates through his or her body. Although the average cord has two arteries, some have only one, which might not cause a problem. This can, however, sometimes indicate the presence of a chromosomal abnormality or a birth defect. In addition, umbilical cord complications are often observed in stillbirths, which is why most doctors offer in-depth testing during pregnancies with an abnormal cord.
In most pregnancies, the umbilical cord is attached to the center of the placenta, but it might instead connect to the fetal membranes, leaving the vessels exposed. This makes them likely to rupture because they are not protected by the Wharton's jelly, and the result is that the baby suffers from low birth weight, premature delivery or stillbirth. Another issue related to the placement of the cord is vasa previa, in which the vessels cross the cervix just beneath the fetus, leaving them vulnerable to damage when the cervix dilates. This can be prevented when the issue is detected early in the pregnancy, which is why doctors often run several tests when they do not see a normal umbilical cord.