What is a true knot?

A true knot happens when the umbilical cord loops and ties into a real knot, much like a shoelace. This usually forms early in pregnancy when baby is small and very mobile. In contrast, a false knot is just a bulge or twist in the cord vessels and is harmless.

How common is it?

True knots are uncommon, roughly 1 in 100 pregnancies. Other studies describe a range of 0.3% to 2%.

Why do true knots form? (Risk factors)

Anything that increases fetal movement space or cord length can make knots more likely. Risk factors include:

• Excessively long umbilical cord
• Polyhydramnios or too much amniotic fluid
• Male fetus
• Multiparity or previous births
• Gestational diabetes
• Monoamniotic twins and some procedures like amniocentesis

Can it be diagnosed before birth?

Sometimes. On ultrasound with color Doppler, a classic finding is the “hanging noose” sign, a transverse view of the cord encircled by a loop of cord. Even so, many true knots are not seen until delivery, and ultrasound can have false positives.

Does a true knot harm the baby?

Most true knots stay loose and cause no problems. If a knot tightens, it can compress the cord vessels, reducing blood and oxygen to the baby. Studies show an increased risk of fetal distress and stillbirth, though most babies with true knots are born healthy.

What will your care team do if a knot is suspected?

Closer surveillance may be advised, for example non-stress tests, Doppler studies, and growth checks. During labor, continuous fetal heart rate monitoring helps catch signs of distress early. Detection alone is not an automatic reason to deliver, since decisions depend on the baby’s wellbeing and the clinical picture.

When should you seek care?

Anytime you notice reduced fetal movements after about 24 to 28 weeks, contact your healthcare provider or maternity unit the same day. Decreased movement can be a sign a baby needs checking, whatever the cause.

Quick Facts

• A true knot is a real cord knot, while a false knot is harmless.
• It occurs in about 1% of pregnancies, with reports ranging between 0.3% and 2%.
• Long cords, polyhydramnios, male fetuses, and multiparity increase the risk.
• Ultrasound may suggest a knot, but many are only confirmed at birth.
• Most are harmless, but a tight knot can reduce blood flow and raise the risk of distress or stillbirth. Monitoring and timely medical care are the keys to safety.

References

• The Fetal Medicine Foundation – Umbilical cord knot: prevalence, ultrasound “hanging noose” sign, follow-up and management guidance.
• PubMed, 2025. Risk factors and outcomes of true umbilical cord knot.
• Ultrasound Obstet Gynecol, 2004. “Hanging noose” sign of umbilical cord knot.
• Systematic Review, 2022. True knots and risk of stillbirth.