Umbilical Cord Prolapse

Umbilical cord prolapse occurs when the cord descends through the cervix alongside the presenting part (occult prolapse) or past it into the vagina (overt prolapse) after the membranes have ruptured. The cord may be visible at the introitus, palpable during a vaginal examination, or hidden beside the presenting part. The danger is mechanical compression. The presenting part can press the cord against the cervix or bony pelvis, while uterine contractions intermittently tighten that pressure. Blood flow through the umbilical vessels then falls, reducing fetal oxygen delivery and causing hypoxaemia, acidosis, and potentially death. This is why the fetal heart-rate pattern may deteriorate abruptly rather than gradually. Cord prolapse is uncommon—approximately 1 to 6 cases per 1,000 births—but the risk is higher with breech presentation. Situations that leave space for the cord to descend include a high or unengaged presenting part, breech or other non-vertex presentation, transverse or oblique lie, prematurity, polyhydramnios, multiparity, and second-twin presentation. Artificial rupture of membranes is a particular hazard when the presenting part is high or mobile. Vaginal manipulation after membrane rupture and procedures such as...