The placenta completely covers the cervical opening at 15 weeks of pregnancy without abnormal symptoms is not considered serious, with the increase of pregnancy weeks may move up to the normal position, after that the position has not been changed is more serious, will increase the chances of prenatal and postpartum hemorrhage. The lower edge of the placenta completely covers the endocervical os, which belongs to complete placenta previa, and is called placenta previa at 15 weeks of pregnancy. With the growth of pregnancy, the lower segment of the uterus is gradually elongated, and the position of the placenta gradually moves upward, transforming it into a borderline placenta previa or a placenta with a normal position, and it is not considered to be very serious if there is no abnormal vaginal bleeding during this period of time. However, if the placenta still completely covers the endocervical os by the 28th week of pregnancy, it will be diagnosed as placenta praevia, and painless and unsignificant vaginal bleeding may occur at any time, increasing the chances of preterm delivery of the fetus, prenatal and postnatal hemorrhage, which is a more serious situation and requires attention in the late stages of pregnancy, and prompt attention to medical treatment if there is any vaginal bleeding.