Overview
Pathophysiology & Epidemiology
Placental implantation occurs when the blastocyst embeds in the lower uterine segment, allowing chorionic villi to lie directly over the internal cervical os.
Placental implantation occurs when the blastocyst embeds in the lower uterine segment, allowing chorionic villi to lie directly over the internal cervical os. As the third trimester progresses the lower segment thins and the cervix begins to efface; the tenuous attachment tears easily, exposing maternal spiral arteries and producing brisk, painless bleeding. The condition is uncommon but its incidence is climbing, driven largely by the rising rate of prior cesarean sections and other uterine surgeries. Each previous cesarean adds a dose‑dependent risk of abnormal placental implantation, and a previous previa raises recurrence to 4–8 % [1].