When Does The Umbilical Cord Form? Guide

The umbilical cord is your baby’s lifeline during pregnancy. It forms early, before many women even know they are pregnant. The cord begins to develop around week 5 of pregnancy and is fully functional by week 8. By the end of the first trimester, it has a clear structure with two arteries and one vein. This guide explains when the cord forms, how it works, and what can go wrong.

When Does The Umbilical Cord Form?

The umbilical cord starts forming at about week 5 of pregnancy. This is roughly three weeks after conception. At this stage, the embryo is tiny — about the size of a pen tip. The structures that will become the cord and placenta are already developing from the same early tissues.

By week 8, the cord is fully formed and functioning. It connects the embryo to the placenta, which is attached to the uterine wall. The cord carries oxygen and nutrients from your blood to the baby. It also carries waste products away from the baby.

This early development happens before most pregnancy symptoms appear. Many women do not even know they are pregnant when the cord begins forming. That is why prenatal vitamins are recommended before conception — the cord and other vital structures form before a missed period.

What Is the Umbilical Cord Made Of?

The umbilical cord has a simple but critical structure. It contains three blood vessels: two arteries and one vein. These vessels are surrounded by a protective substance called Wharton’s jelly. This jelly-like material cushions the vessels and prevents the cord from kinking or compressing.

The two arteries carry deoxygenated blood and waste products from the baby to the placenta. The placenta filters these wastes and picks up fresh oxygen and nutrients from your blood. The single vein carries this oxygen-rich blood back to the baby.

At full term, the cord is typically about 50 to 60 centimeters long — roughly 20 to 24 inches. It is about 1 to 2 centimeters in diameter. The cord continues to grow throughout pregnancy as the baby grows.

How Does the Umbilical Cord Develop Week by Week?

The cord develops through several distinct stages. Understanding these stages helps explain why early prenatal care matters.

Weeks 3 to 4: The Beginning

After fertilization, the embryo implants in the uterine lining. Cells begin dividing rapidly. Some cells will become the baby. Other cells will become the placenta and cord. At this point, there is no visible cord — just a cluster of developing cells.

Weeks 5 to 6: The Cord Appears

The body stalk, which is the primitive cord, becomes visible. Blood vessels begin forming within it. The heart — which is also developing — starts beating around this time. The cord is short and thick at this stage.

Weeks 7 to 8: The Cord Matures

The cord lengthens and becomes more defined. Wharton’s jelly forms around the blood vessels. The three-vessel structure is now established. Blood flow through the cord is active and continuous.

Weeks 9 to Term: Growth and Change

The cord grows longer as the baby grows. It coils and twists naturally. Most cords develop a spiral appearance. By the second trimester, the cord has its full structure. It will continue to lengthen until about week 28.

What Does the Umbilical Cord Do?

The cord is the only connection between you and your baby. It performs three essential jobs.

• Delivers oxygen: Oxygen from your blood moves across the placenta into the cord’s vein and reaches the baby.
• Delivers nutrients: Glucose, amino acids, vitamins, and minerals all travel through the cord to the baby.
• Removes waste: Carbon dioxide and other waste products travel through the cord’s arteries back to the placenta, where your body removes them.

The cord does not mix your blood with the baby’s blood. The placenta acts as a barrier between your circulatory system and the baby’s. Only small molecules like oxygen, nutrients, and some antibodies cross this barrier. Larger cells, like red blood cells, do not normally cross.

What Conditions Can Affect the Umbilical Cord?

Several conditions can involve the umbilical cord. Some are common and harmless. Others require monitoring. Knowing the facts helps you understand what your doctor is checking during ultrasounds.

Nuchal Cord

A nuchal cord means the cord is wrapped around the baby’s neck. This is common — it occurs in about 20 to 30 percent of births. Most nuchal cords are harmless. The cord is slippery and can often be slipped over the baby’s head during delivery. In rare cases, a tight nuchal cord can affect heart rate during labor, and medical staff are trained to manage this.

Single Umbilical Artery

Normally, the cord has two arteries and one vein. About 1 percent of cords have only one artery. This is called a single umbilical artery. It is sometimes associated with other congenital conditions. Doctors will often recommend additional ultrasounds if this is found. However, many babies with a single umbilical artery are born completely healthy.

True Knots

A true knot in the cord is exactly what it sounds like — the cord ties itself in a knot. This is rare, occurring in about 1 percent of pregnancies. Most true knots do not tighten enough to cause problems. However, a knot that tightens can reduce blood flow. This is why fetal movement monitoring matters in the third trimester.

Cord Prolapse

Cord prolapse happens when the cord slips into the birth canal before the baby during delivery. This is an emergency because the baby’s weight can compress the cord and cut off blood flow. It occurs in fewer than 1 percent of births. If it happens, doctors perform an immediate cesarean delivery.

When Is the Umbilical Cord Clamped and Cut?

After birth, the cord is clamped and cut. This happens in the first minutes of life. The timing of clamping has changed in recent years.

Delayed cord clamping is now standard practice in most hospitals. This means waiting 30 to 60 seconds after birth before clamping. This delay allows extra blood to flow from the placenta to the baby. Research shows this extra blood provides iron and improves iron stores in the first months of life.

The remaining stump of cord attached to your baby’s belly button will dry up and fall off. This usually happens within one to three weeks after birth. Keep the stump clean and dry. Do not pull it off — let it fall off naturally.

Can You Prevent Umbilical Cord Problems?

Most cord problems cannot be prevented. They occur randomly during development. You cannot control whether the cord wraps around the neck or forms a knot. These events are not caused by anything you do or do not do.

What you can do is monitor fetal movement in the third trimester. A sudden decrease in movement can sometimes indicate a cord problem. If you notice fewer movements than usual, contact your healthcare provider immediately. They can check the baby’s heart rate and blood flow with ultrasound.

Regular prenatal visits are also essential. Your doctor will check the cord during routine ultrasounds. Most cord issues are found during these scans, not because of symptoms.

What Happens to the Umbilical Cord After Birth?

After the baby is born and the cord is clamped, the placenta is delivered. This usually happens within 5 to 30 minutes after birth. The placenta and cord are examined by medical staff to ensure they are complete and healthy.

Cord blood — the blood remaining in the cord and placenta after birth — contains stem cells. Some parents choose to bank this blood for potential future medical use. Private cord blood banking costs money. Public cord blood donation is free and can help others. Neither option is medically necessary for a healthy baby.

The cord itself has no further function after birth. The baby’s own circulatory system takes over immediately. The belly button that remains is simply the scar from where the cord was attached.