Overview
Definition and Mechanism
Umbilical cord prolapse occurs when the cord descends through the cervix alongside or past the fetal presenting part after the membranes have ruptured.
Umbilical cord prolapse occurs when the cord descends through the cervix alongside or past the fetal presenting part after the membranes have ruptured. In an occult prolapse, the cord lies beside the presenting part and may not be visible or palpable; in an overt prolapse, it passes beyond the presenting part and may be felt in the vagina or seen at the introitus. Both are emergencies because the presenting part can compress the cord against the maternal pelvis. Cord presentation is different: the cord lies between the presenting part and the cervix while the membranes are still intact. It is not yet cord prolapse, but membrane rupture can convert it rapidly into one. Injury results first from mechanical compression. The cord is compressed like a soft tube caught between the fetal head or breech and a hard pelvic surface, reducing venous and arterial flow. Cold ambient air and repeated handling of an exposed cord add umbilical-vessel vasospasm. The combined effect can produce acute fetal hypoxaemia, bradycardia, and acidaemia; prolonged compression may lead to hypoxic-ischaemic encephalopathy, seizures, or death.