The placenta is considered normal when it is >2cm from the cervical opening. The placenta is considered to be in a normal position when it is >2cm from the endocervical opening after pregnancy. After the formation of the placenta, it covers about 1/2 of the uterine cavity in mid-pregnancy and 1/3 or 1/4 in late pregnancy. When the lower part of the uterus is formed, the distance between the edge of the placenta and the endocervical os is increased appropriately, and the placenta attached to the lower part of the uterus can be gradually moved upward to the placenta in a normal position. In mid-pregnancy when ultrasound suggests that the lower edge of the placenta is close to or reaches the endocervical os, it is necessary to pay attention to appropriate rest, prohibit coitus, and follow the doctor’s instructions for timely ultrasound. With the formation of the lower segment of the uterus and the enlargement of the uterus, the relationship between the edge of the placenta and the endocervical os will change, and most of them can gradually move up to the normal position. However, when the placenta is still suggestive of low placenta after 28 weeks of pregnancy, pregnancy management should be strengthened.