The umbilical cord is a flexible, rope-like structure that connects a developing baby to the placenta inside the uterus. It serves as the baby’s lifeline throughout pregnancy, delivering oxygen and nutrients from the mother’s bloodstream and carrying waste products back out. By the end of the second trimester, a typical cord measures about 50 to 60 centimeters (roughly 20 to 24 inches) long and is less than an inch in diameter.
What’s Inside the Cord
A normal umbilical cord contains three blood vessels: two arteries and one vein. The vein carries oxygen-rich blood and nutrients from the placenta to the baby. The two arteries carry deoxygenated blood and waste products from the baby back to the placenta, where carbon dioxide and other byproducts pass into the mother’s circulation for disposal.
These vessels are surrounded by a soft, gel-like connective tissue called Wharton’s jelly. This jelly is porous and filled with fluid, and its main job is mechanical protection. It cushions the blood vessels against compression, which matters because the cord is constantly being twisted, squeezed, and looped as the baby moves. Wharton’s jelly also adjusts its thickness as the vessels expand and contract, preventing them from stretching too far. The outermost layer is a thin membrane called the amnion, which wraps the entire structure in a smooth, slippery coating.
How the Cord Nourishes the Baby
A baby in the womb can’t eat, breathe, or filter waste on its own. The umbilical cord handles all three functions. Oxygen crosses from the mother’s blood supply through the placenta and travels through the cord’s single vein to reach the baby. At the same time, glucose, fats, proteins, vitamins, and minerals pass through the same route. Carbon dioxide and metabolic waste travel the opposite direction through the two arteries.
The placenta acts as a selective barrier. It allows smaller molecules like oxygen and glucose through while keeping the mother’s and baby’s blood supplies separate. The cord is simply the transport highway between the placenta and the baby’s body, with blood continuously circulating in both directions throughout pregnancy.
Common Cord Variations
Not every umbilical cord looks or behaves the same, and most variations are harmless. A nuchal cord, where the cord wraps around the baby’s neck, is present in about 22% of births. That number surprises many parents, but in the vast majority of cases it causes no problems and is managed easily during delivery.
True knots in the cord, where the baby’s movement causes the cord to tie into an actual knot, occur in roughly 1% of births. Most true knots remain loose enough that blood flow isn’t affected. Cord prolapse, where the cord slips ahead of the baby into the birth canal before delivery, is much rarer at about 0.17% of pregnancies, but it requires immediate medical attention because the baby’s body can compress the cord and cut off blood flow.
The spot where the cord attaches to the placenta also varies. Ideally, it inserts near the center. In marginal cord insertion, the cord attaches within 2 centimeters of the placenta’s edge instead. This is usually detected on ultrasound and monitored, though many pregnancies with marginal insertion proceed normally.
What Happens at Birth
Once the baby is born and begins breathing on its own, the umbilical cord is no longer needed. It’s clamped in two places and cut between the clamps. The baby feels nothing during this process because the cord has no nerves.
The timing of clamping has shifted in recent years. The American College of Obstetricians and Gynecologists recommends waiting at least 30 to 60 seconds after birth before clamping in healthy term and preterm infants. This brief delay allows additional blood to transfer from the placenta to the baby, which helps boost iron stores and blood volume in the newborn. Immediate clamping is still done when the situation calls for it, such as when the baby needs urgent medical care.
Caring for the Stump
After the cord is cut, a small stump remains attached to the baby’s belly. This stump dries out and typically falls off on its own within 5 to 15 days. The area underneath becomes the belly button.
Stump care is straightforward. Keep it clean using only gauze and water. Fold diapers below the stump so air can reach it, and stick to sponge baths rather than tub baths until the stump detaches. Don’t try to pull it off, even if it looks like it’s barely hanging on. Signs of a problem include redness, swelling, a foul smell, or oozing around the base, which could indicate infection.
Cord Blood Banking
The blood remaining in the umbilical cord and placenta after birth contains a rich supply of stem cells. These are immature cells capable of developing into various types of blood and immune cells. Cord blood stem cells are already used to treat certain blood disorders, including leukemia, Hodgkin disease, and some types of anemia. They can also treat specific inherited metabolic and immune system disorders.
Parents can choose to bank cord blood either in a public bank, where it becomes available to anyone who needs a stem cell transplant, or in a private bank, where it’s stored exclusively for the family. Public banking is free and donation-based. Private banking involves collection fees and annual storage costs. The collection process is painless and happens after delivery, posing no risk to the mother or baby.