The normal attachment of the placenta is to the posterior, anterior, or lateral wall of the uterine body. If the placenta is attached to the lower segment of the uterus or covers the internal os of the cervix, and is positioned lower than the presenting part of the fetus, it is called placenta previa. This disease is one of the main causes of bleeding in the second and third trimesters of pregnancy and is also a serious complication during pregnancy. If handled improperly or not in time, the life safety of mother and baby will be endangered. Symptoms of placenta previa are characterized by painless vaginal bleeding that often recurs. There is no sign before bleeding, and it often occurs in the middle of the night, and the patient wakes up due to vaginal bleeding. Generally speaking