Notching of the umbilical artery waveform associated with cord entanglement in a monoamniotic twin pregnancy.

Cord accidents are the principal cause of the high rates of morbidity and mortality associated with monoamniotic twins. Observation of an umbilical artery notch might be a highly specific sign for cord entanglement involving a tight cord knot. It thus justifies the implementation of intense surveillance and should be one of the factors taken into account in deciding on early delivery of the twins.