The umbilical cord is a narrow, tube-like structure that connects the
developing baby (also referred to, in medical terms, as the fetus) to
the placenta and transports blood and nutrients between the placenta and
the fetus and back. The umbilical cord begins to form at 5-6 weeks after conception and then becomes progressively longer until 28 weeks of pregnancy, reaching an average length of 22 to 24 inches. As the cord gets longer, it generally coils around itself either clockwise or counterclockwise.
The umbilical cord contains three blood vessels: two arteries and one vein.
The umbilical vein carries oxygen and nutrients from the placenta (which connects to the mother's blood supply) to the baby.
The two umbilical arteries transport waste from the baby to the placenta (where waste is transferred to the mother's blood and disposed of by her kidneys).
A gelatin-like tissue called Wharton's jelly cushions and protects these blood vessels.
Umbilical cord anomalies are frequent and when they happen there are often increased risks to the pregnancy:
- The cord is too long (5% are over 80 cm)
- The cord is too short (5% are under 35 cm)
- The cord is too thin
- The cord connects improperly to the placenta
- The cord becomes knotted or compressed
- There is only one arterty instead of two (single umbilical artery)
- The blood vessels travel through the membranes (velamentous insertion)
- The cord wraps around the fetus' neck or other body parts
Cord abnormalities can lead to problems during pregnancy or during labor and delivery. In some cases, cord abnormalities are discovered after delivery when a doctor examines the cord and the placenta.