What is the Cause of Umbilical Cord Knots?

An umbilical cord knot, as the name implies, is a tie in the baby’s umbilical cord. Since the umbilical cord is responsible for carrying nutrients from the placenta to the baby, any kinks in the system can prove dangerous. Though the vast majority of these umbilical cord knots are harmless, some can constrict the flow of nutrients and lead to fetal harm.

How Common are Umbilical Cord Knots?

Knots of the umbilical cord are relatively common, occurring in about one in every 100 pregnancies. A far more common occurrence is a nuchal loop – the technical term for when the umbilical cord wraps around the baby’s neck. These occur in up to a quarter of all pregnancies, and like umbilical cord knots, rarely pose a threat to the baby.

How do Umbilical Cord Knots Occur?

During pregnancy, a developing baby kicks and turns in his or her mother’s belly. Over time, these fetal movements can lead to knots in the cord. Since fetuses move naturally throughout the woman’s womb in pregnancy, it’s natural that these knots might occur.

Umbilical cord knots do have certain risk factors, however. A baby might be at higher risk for an umbilical cord knot:

  • If he or she is a monoamniotic twin, or shares a sac with another baby
  • If the mother has polyhydramnios, or too much amniotic fluid
  • If the umbilical cord is longer than usual
  • If a fetus is smaller than usual
What are the Signs and Symptoms of an Umbilical Cord Knot?

Mothers generally undergo careful monitoring throughout the course of a pregnancy. Each appointment includes the assessment of a fetal heart rate, and women experience periodic ultrasounds as part of their preventive treatment. The presence of an abnormal heart rate may be a sign of a true umbilical cord knot, while some knots may appear on routine imaging. In some cases, decreased fetal activity reported by the mother is the first sign of an umbilical cord issue.

Umbilical Cord Knots: When to Worry

Most umbilical cord knots pose no threat to a developing baby, especially with careful monitoring. The umbilical cord contains an important substance, called Wharton’s jelly, that provides cushioning to the available vessels and protects the structure, even when a knot occurs. As the result of this jelly, it’s unlikely that a true, tight, “knot” will occur. If the knot remains loose and there’s no constriction to the cord, then it’s safe for the baby.

On the other hand, umbilical cord knots can present a risk to a baby when the loop tightens and interferes with the blood flow from the placenta to the baby. In this instance, it can lead to oxygen deprivation, brain damage, or even stillbirth. A complication is most likely to occur during the delivery process and descent into the birth canal.

Treating a Knot in the Umbilical Cord

Unfortunately, there's nothing that moms or providers can do to prevent the onset of an umbilical cord knot. However, early recognition and intervention are essential. It’s important for mothers to keep all their prenatal appointments and complete their own fetal monitoring by completing kick counts. Fewer than 10 fetal movements in two hours merits a call to a provider.

When a loose umbilical cord knot tightens as the baby descends into the birth canal, fetal monitoring may detect an abnormal heart rate. In this case, a provider will decide on the best way to protect the baby. Often, this is an immediate delivery of the baby via an emergency cesarean section. Failure to intervene at the appropriate time could lead to oxygen deprivation and subsequent brain damage.