Umbilical Cord Knot

Umbilical cord knots are true knots (a loop of cord passes through itself) or false knots (focal vascular redundancy or varicosity of the cord vessels, which are harmless). True knots occur in 0.3 to 2% of pregnancies and are associated with long cords (above 80 cm), male fetuses, polyhydramnios, small fetuses, monoamniotic twins (up to 70%), multiparity, advanced maternal age, gestational diabetes and external cephalic version.

Trouble arises when the knot tightens and compromises blood flow: stillbirth risk is raised about 4-fold (a knot is found in 4 to 10% of stillbirths), with growth restriction, low Apgar scores and fetal heart rate abnormalities, but most knots are loose and harmless.

• Usually asymptomatic until labour
• Reduced fetal movements in some tight knots
• Variable or prolonged decelerations, fetal bradycardia and meconium stained liquor in labour
• At birth: knot visible with a groove in the cord and venous congestion beyond the knot; neonatal depression if tight

• Antenatal ultrasound with colour Doppler: the "hanging noose" or "cloverleaf" sign suggests a true knot, but sensitivity is low and the finding is usually incidental; 3D and 4D ultrasound can help
• Cardiotocography with persistent variable decelerations
• Diagnosis is usually made at delivery or on placental pathology (knot with a groove and congestion)
• In monoamniotic twins, ultrasound for cord entanglement

• An incidental knot in a well fetus needs no intervention, and routine early delivery is not indicated
• Counsel on fetal movement monitoring; reduced movements need cardiotocography and ultrasound for growth and Doppler the same day
• Suspected tight knot (growth restriction, abnormal Doppler or cardiotocography): fetal surveillance with delivery at term, or earlier if tests are abnormal
• Labour: continuous electronic fetal monitoring when risk factors exist; expedite delivery (caesarean or operative vaginal) for a prolonged abnormal heart rate pattern
• Monoamniotic twins carry a high risk of entanglement and need specialised surveillance and planned caesarean delivery at 32 to 34 weeks
• Neonatal resuscitation team ready at delivery; cord blood gases
• Record the finding, and send the placenta for histology after any adverse outcome