Umbilical Cord Prolapse

Umbilical cord prolapse occurs when, after the membranes have ruptured, the cord descends through the cervix alongside or past the presenting part. An occult prolapse lies beside the presenting part and may not be visible; an overt prolapse extends below it and may be seen at the introitus or felt during a vaginal examination. The presenting part can act like a clamp, trapping the cord against the cervix or maternal pelvis. Compression reduces blood flow through the cord and can deteriorate fetal oxygenation within minutes. Intermittent compression commonly produces abrupt variable decelerations. Sustained or severe compression may produce a prolonged deceleration or bradycardia, followed by metabolic acidosis and hypoxic injury if birth is not expedited. Risk is greater when the presenting part does not fill the pelvic inlet. Important examples include a high or unengaged presenting part, breech or other non-vertex presentation, transverse or oblique lie, prematurity, polyhydramnios, multiparity, preterm premature rupture of membranes, external cephalic version, and the presenting part of a second twin. Artificial rupture of membranes and upward displacement during a vaginal examination can precipitate prolapse when...