The lower edge of the placenta is greater than 30 mm from the internal cervical os, which is the normal position. If the placenta is hypoplastic, the lower border of the placenta is less than 20 mm from the endocervix. in the middle of pregnancy, if the placenta is hypoplastic, most of them will return to the normal position after 7 months of pregnancy. If after 7 months of pregnancy, the lower edge of the placenta is still less than 20mm from the endocervix or appears to cover the endocervix, then the placenta is hypoplastic or placenta praevia, which is abnormal and cannot be delivered vaginally and requires a cesarean section. If that distance is more than 30mm, it has no effect on the delivery.