Various doctrines involve the most damage to the endometrium. When the fertilized egg is deposited in the lower uterine segment of the cesarean section scar and there is a defect in the endometrial surface of this part of the uterus, the chorionic cells will invade the myometrium directly and form an intramyometrial pregnancy. Development trend: 1, chorionic villi planted in the cesarean section scar indentation continuously infiltrate into the myometrium: cesarean section scar pregnancy that grows toward the intermuscular wall can occur uterine rupture, perforation, and hemorrhage early in the gestation period, and can be fatal and hemorrhagic if it is not treated in time. 2. Chorionic villi grow from the cesarean section scar into the uterine cavity: 40% of the patients have placental adhesion or implantation, which can cause uterine rupture or hemorrhage during delivery.