Umbilical Cord

Understanding umbilical cord development

The umbilical cord (also called the birth cord) connects the developing fetus to the placenta. It functions as a lifeline, connecting the vulnerable fetus to its mother and delivering vital nutrients and oxygen, while carrying away waste materials.

Umbilical cord development begins around the fifth week of the embryonic period of fetal development. The umbilical cord is derived from the yolk sac and allantois (which, in turn, were derived from the same zygote that the fetus develops from) and replaces the yolk sac as the fetus' source of nutrients.


A fully-developed umbilical cord is typically between 18 and 24 inches in length and nearly an inch in diameter. It contains three distinct blood vessels: one vein (that carries oxygenated and nutrient-rich blood to the fetus) and two arteries (that carry depleted blood away from the fetus).

The umbilical cord is coated in a substance called Wharton's jelly, which serves to strengthen the cord and protect the blood vessels inside.

The maternal end of the umbilical cord is attached to the placenta, which acts as an intermediary between the umbilical cord and the mother's circulatory system. The other end attaches to the fetus in the abdominal area (what will later become a person's navel or "belly button"). Inside the developing fetus, a small portion of blood from the umbilical cord is delivered to the liver via the hepatic portal vein and a larger portion is delivered to the heart via the inferior vena cava (and then pumped to the developing fetus' extremities).

Umbilical cord blood contains stem cells that can be used to treat some immune disorders and cancers, so it is sometimes collected after the cord has been cut from the newborn baby. Cord blood banking is the name given to the practice of preserving umbilical cord blood, so that it will be available to use in the future (should a medical condition arise that would respond favorably to treatment with cord blood).

Umbilical Cord Complications

There are a number of potential problems that can arise during the development of the fetus that involve the umbilical cord, such as:

  • Nuchal Cord: A relatively common problem during fetal development that occurs when the umbilical cord becomes wrapped around the fetus' neck. A type A nuchal cord is wrapped around the entire 360 degrees of the fetus' neck. A type B nuchal cord is wrapped in a "hitch" pattern and cannot be unknotted.
  • Single Umbilical Artery: The most common umbilical cord complication, this occurs when the umbilical cord contains only a single artery (rather than the usual two), in addition to a single vein. Although this condition increases the likelihood of congenital abnormalities, most fetuses with SUA do not experience any other problems.
  • Umbilical Cord Prolapse: This is a rare complication that occurs when the umbilical cord exits the uterus prior to the fetus during labor. This can cut off the supply of oxygen and blood to the fetus.
  • Velamentous Cord Insertion: In this rare umbilical cord complication, the cord doesn't connect directly to the placenta, but instead connects to the fetal membranes and then travels within these membranes to the placenta, resulting in exposed vessels that are vulnerable to rupture.