Tracing shows late decels: the bad kind, a response to poor blood flow to the fetus during contractions. One cause, particularly common after AROM, is umbilical cord prolapse, where the fetal head compresses the umbilical cord, limiting blood flow as it’s squeezed inferiorly by the contracting uterus. Vertex station doesn’t actually matter as once previously thought, but a nondilated cervix (less than 6 cm) is a risk factor.

Prolapse of the cord often leads to cord compression which, in turn, leads to abnormal findings on fetal heart rate (FHR) tracings in 41% to 67% of cases. These changes may present as a severe, sudden deceleration, often with prolonged bradycardia, or recurrent moderate-to-severe variable decelerations

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