Master the 2026 Certified Obstetric Emergencies Exam – Deliver Your Success with Confidence!

Chorionic villi in placenta accreta attach to the myometrium, the muscular layer of the uterus, because the decidua basalis is defective or absent. Normally these villi anchor to the decidua basalis within the endometrium, but when that layer is inadequate, the villi stick directly to the myometrium. This abnormal adhesion explains why placenta accreta can be difficult to detach after delivery and lead to heavy bleeding. The other structures listed aren’t the site of abnormal attachment in this condition: the endometrium is the usual site of placental attachment, the serosa is the outer uterine surface and not involved here, and the placental disk is part of the placenta itself, not the uterine wall where adhesion occurs.