The normal range of the lower edge of the placenta close to the endocervical os should be more than 2cm, the lower edge of the placenta less than 2cm from the endocervical os is placenta praevia, the lower edge of the placenta reaches to the endocervical os but not beyond the endocervical os is limbic placenta, the lower edge of the placenta partially covers the endocervical os is partially placenta praevia, and the lower edge of the placenta completely covers the endocervical os is complete placenta praevia. Placenta praevia is prone to cause painless bleeding in late pregnancy. If painless vaginal bleeding occurs, ultrasound should be performed to rule out placenta praevia. If the placenta is found to be in a low position with vaginal bleeding during pregnancy, you should go to the hospital in time. During labor, you should make good preparations for postpartum hemorrhage and prepare blood in advance to prevent intrauterine distress of the fetus and the occurrence of hemorrhagic shock.