What are abnormalities of placental implantation?

➢ Placenta previa is a condition in which the placenta implants in the lower uterine segment or cervix, often leading to serious thirdtrimester bleeding. – A complete placenta previa covers the internal cervical os →requires delivery via cesarean section to avert placental rupture and fatal maternal hemorrhage during vaginal delivery. ➢ Placenta accreta: is caused by partial or complete absence of the decidua, → the placental villous tissue adheres directly to the myometrium → failure of placental separation at birth. – Important cause of severe, potentially lifethreatening postpartum bleeding. – Common predisposing factors : placenta previa (in up to 60% of cases) and history of previous cesarean section