There are three varieties of cord prolapse:
Overt cord prolapse - if the presenting part of the fetus does not fit the pelvis snugly after membrane rupture, there is a risk that the umbilical cord can slip past and present at the cervix or descend into the vagina. This is known as overt cord prolapse. It represents an acute obstetric emergency, as prolapse exposes the cord to intermittent compression compromising the fetal circulation. Depending on its duration and degree of compression, fetal hypoxia, brain damage and even death can occur. Exposure of the umbilical cord to air causes irritation and cooling, resulting in vasospasm of the cord vessels.
This is a companion discussion topic for the original article at https://patient.info/doctor/obstetrics/prolapsed-cord