There is a risk of the lower edge of the placenta reaching the inner cervical os. Special clinical attention should be paid to this condition. Pregnant women should not have sexual intercourse, which may result in hemorrhage due to detachment between the edge of the placenta and the uterine wall after sexual intercourse, and pregnant women should not do strenuous exercise. As the pregnancy progresses further, the lower part of the uterus is formed at about 16 weeks of pregnancy and the placenta gradually extends towards the uterine fundus. Placenta praevia is clinically diagnosed at 28 weeks of pregnancy if the lower edge of the placenta is <7cm from the inner cervical opening. Placenta praevia often causes painless and sudden heavy bleeding in clinical practice, so pregnant women should go to the hospital for examination as soon as bleeding occurs.