Ordinary ultrasound can show the distance between the placenta and the cervical opening, which needs to be operated by a specialized doctor. Placenta praevia is a serious complication of pregnancy. For pregnant women with high risk factors such as a history of multiple miscarriages, uterine operations, or cesarean section, ultrasound should be performed after a second pregnancy to assess the position of the placenta in relation to the opening of the cervix, so that placenta praevia can be detected as early as possible, and to enhance the management of pregnancy. Ordinary ultrasound can also show the distance between the placenta and the cervical opening, which needs to be operated by a specialized doctor. When the ultrasound suggests that the lower edge of the placenta is >2.0cm from the endocervical os, it is a normally positioned placenta. Generally, when the ultrasound examination in the middle of pregnancy suggests that the lower edge of the placenta is close to or reaches the endocervical opening, it is the state of placenta previa, and dynamic observation of changes in the position of the placenta is required. With the enlargement of the uterus and the formation of the lower segment of the uterus, most of the placenta previa can be restored to its normal position. Consult your physician for specific advice.