The umbilical cord is a three-vessel cord that provides nutrients and oxygen to your baby while they're in the uterus. Usually, the cord doesn’t have any issues, but there are several conditions that may impact the effectiveness of your baby’s umbilical cord. Learn more about these abnormalities and find out when you should be concerned.
Understanding the Umbilical Cord
Your baby’s umbilical cord connects from their navel to the placenta, a special organ that grows during pregnancy to facilitate moving blood, oxygen, and nutrients from you to your baby.
Your baby’s umbilical cord has three layers:
- Tunica externa – this outermost layer is made of a dense elastic-like fiber to protect the cord.
- Tunica media – the middle layer contains a majority of the umbilical cord’s blood vessels. It helps to regulate your baby’s blood flow and blood pressure.
- Tunica interna – this connective tissue has valves controlling blood flow. It ensures deoxygenated blood moves to the placenta and oxygenated blood moves back to your baby
Single Umbilical Artery
Your baby’s umbilical cord should have two arteries and one vein. It is often referred to as a three-vessel cord. Sometimes one of the arteries is missing, usually the left one. If your umbilical cord only has one artery, it increases your risk for fetal anomalies.
Single umbilical artery risks. Single artery umbilical cord problems only happen in around 1% of pregnancies, although the risk increases to 5% for twin pregnancies. A lack of one vessel is called a two-vessel cord. This condition increases the risk of:
- You having high blood pressure toward the end of your pregnancy
- Your baby being smaller than average
- Infant death soon following birth
- Trisomy 18
- Cardiovascular abnormalities
- Gastrointestinal issues
- Esophageal atresia
- Kidney problems
Causes of single umbilical artery. The cause is largely unknown. White women are twice as likely to develop this condition compared to other races. You’re also more likely to have a single artery umbilical cord if you have been diagnosed with diabetes.
Diagnosing a single umbilical artery. The two arteries and one vein are easily identifiable on ultrasounds during your pregnancy. Usually, the vein is larger and distinguishable from the two arteries. A technician may note that there is only a single artery after looking at a cross-section of your umbilical cord. They may also note that an artery is only seen on one side of your baby’s bladder.
Vasa previa is a condition that occurs when the fetal vessels attach near the cervix. This condition is dangerous because the cord may rupture when your water breaks during labor. In twins, it may occur near the membrane that divides your infants from one another in the womb.
Risks of vasa previa. During pregnancy, this condition doesn’t pose any risks. However, if the vessels tear during labor, there is a 50-75% chance your baby doesn’t survive during delivery. Even if vessels don’t tear, the pressure of labor may reduce oxygen during delivery and put your baby at risk for distress.
Causes of vasa previa. It occurs in fewer than one in 3,000 deliveries. The cause is greatly unknown, although it is associated with a low-lying placenta, a placenta containing accessory lobes, and if you’re carrying more than one baby.
Diagnosing vasa previa. This condition is often identified using ultrasound imaging during your pregnancy. If it isn’t identified on an ultrasound, it may become evident during labor if your baby’s heart rate drops. If your doctor diagnoses vasa previa, they may recommend a cesarean delivery between 34-37 weeks.
If your baby’s umbilical cord wraps around their neck, it is called a nuchal cord. This condition affects 20-30% of pregnancies and 5% of cases involving multiple loops around the neck.
Risks of nuchal cord. Most of the time, this condition won't cause any issues. In rare cases, you may need labor induction to ensure a prompt delivery. A nuchal cord also leaves you at risk for a longer labor and your baby at risk for a decreased heart rate during contractions.
Causes of nuchal cord. When your baby moves around in the womb, the cord easily wraps around different parts of their body. In fact, the cord may wrap and unwrap multiple times throughout your pregnancy as your baby stretches and grows.
Diagnosing a nuchal cord. As with other umbilical cord abnormalities, an ultrasound frequently diagnoses the condition. Nuchal cords can are also diagnosed at the time of birth, especially if it did not cause any issues with the baby's heart rate. If it isn’t diagnosed before labor, it may become obvious if your baby’s heart rate decreases consistently with each contraction.
Umbilical Cord Knots
An umbilical cord knot happens when your baby moves around in a manner that causes a loop in the cord as if it were tied.
Causes of an umbilical knot. Most cord knots are caused by infant movement. However, some factors increase the likelihood of an umbilical cord knot:
- Identical twins sharing a single amniotic sac
- Too little amniotic fluid
- A longer umbilical cord
- A smaller baby that has more room to move
Diagnosing an Umbilical Knot. Most of the time, a knot doesn’t show up on ultrasound imaging. Because the cord is long, parts of it may be covered when a technician is checking your baby. Plus, ultrasound images don’t always provide a clear enough picture to identify a knot.
Your doctor may suspect a knot if your baby’s heart rate is unusually low or inconsistent. Your baby may also be less active than normal if there is a cord knot present.
Risks of a cord knot. Most of the time, an umbilical cord knot doesn’t get tight enough to cause harm to your baby. However, a true knot may cut off blood flow to your baby, leaving them at risk of losing oxygen and nutrients. This may lead to brain damage and even stillbirth. Because vaginal delivery adds stress to your baby, a cord knot may lead to cesarean delivery for a birth free of complications.