What to Know About Umbilical Cord Knots

Medically Reviewed by Traci C. Johnson, MD on April 19, 2023
4 min read

During pregnancy, you are focused on counting down to the birth of your baby. However, there may be concerns that come up during ultrasounds that leave you with doubts and worries. While umbilical cord knots happen in less than 1% of pregnancies, if your baby has one, you may wonder what it means.

The umbilical cord attaches to the placenta, which is an organ that develops during pregnancy to transfer blood, oxygen, and nutrition from mother to baby. In the womb, your baby cannot yet breathe using their lungs. The umbilical cord transfers deoxygenated blood from your baby into the placenta. 

Your baby's umbilical cord has three layers of muscle:

  • Tunica externa: This outer layer is elastic and dense to protect the cord from damage.
  • Tunica media: The middle layer of the cord contains the majority of the blood vessels. It serves to regulate your baby's blood flow and blood pressure.
  • Tunica interna: This is the center of the cord, composed of connective tissue. It contains valves that control blood flow to ensure deoxygenated blood goes into the placenta and oxygenated blood returns to your baby.

Just as the name says, an umbilical cord knot is a place in your baby’s umbilical cord that gets tied. A knot in the cord may cut off much-needed nutrients from reaching your baby, stunting their growth and posing other health problems. Rest assured, most umbilical cord knots don’t end up causing harm to babies in the womb.‌

Reasons for an umbilical knot. During pregnancy, you feel your baby kick and wiggle around all day long. As they stretch and explore their small home inside your womb, it is very easy to knot the cord. Most cord knots happen early on in pregnancy when your baby is still small and has more room to move around. However, there are some factors that increase the chance of a cord knot:

  • Two babies share one sac (identical twins)
  • Not enough amniotic fluid inside your uterus
  • A longer than usual umbilical cord
  • Baby is smaller than average, allowing more room to move around

Signs of an umbilical knot. Most knots don’t show up on ultrasound imaging. This is because the cord is long, and as your baby grows, they may cover part of the cord during ultrasound viewing. Additionally, the ultrasound images aren’t always clear enough to indicate a knot.

However, as the technician monitors your baby’s heart rate and activity, they are checking for signs of an umbilical cord knot. Even if they can't see one visually, they can detect other signs of a problem with blood flow to and from the placenta. For example, if your baby’s heart rate is low or inconsistent, that could be a sign of a cord knot. 

Your baby may also be less active than normal since their nutrient supply is cut off. Be sure to tell your doctor or technician if you've noticed a decrease in your baby's activity inside the womb.

Cord knot concerns. While a majority of cord knots don’t pose a risk for your baby, doctors still monitor your pregnancy closely if one is identified. The cord is designed to prevent a tight knot — also called a “true knot” — from happening. Most knots don't cause problems for your baby.

As long as the knot isn’t too tight, blood flow and nutrients aren’t restricted. However, a tight knot leaves your baby without enough oxygen and puts them at risk for brain damage and even stillbirth.

With the added stress and pressure of giving birth, there’s a chance your baby’s umbilical cord knot can tighten during labor. This is why doctors closely monitor your baby’s heart rate as your body progresses through the stages of labor. If your baby's heart rate drops too much, you may need a cesarean section to prevent more distress. This increases the chance of a safe, healthy delivery without complications.

Addressing a cord knot. Doctors cannot treat an umbilical cord knot, and there isn’t anything you can do to prevent one from happening. However, identifying a knot and closely monitoring your baby can be the difference between a healthy delivery and a potential injury to your baby. Know the signs of a cord knot and talk to your doctor about any concerns you have.

If your doctor identifies a knot on an ultrasound, they may ask you to come in for more frequent ultrasounds and monitoring. They want to check for adequate growth and a strong heartbeat, both signs your baby is thriving in the womb. If you feel your baby kick less than 10 times in a two-hour period, call your doctor right away.