The lower edge of the placenta in the third trimester covers the inner cervical opening, which is a low lying placenta. In the third trimester, the placenta itself usually occupies half of the uterine wall, so there are more chances for the placenta to be close to or cover the endocervical opening. In the second trimester, the placenta occupies less than one-third or one-fourth of the uterine wall, and the formation and extension of the lower uterine segment increases the distance between the endocervical os and the edge of the placenta, so that most of the placenta can move upward with the uterine body to become a normal position of the placenta. Therefore, when the lower edge of the placenta covers the endocervical opening in the third month of pregnancy, in principle, it is not called placenta previa, but should be called placenta hypoplasia. At this time, if there is no clinical discomfort, not accompanied by abnormal vaginal bleeding, you can be observed, and regular ultrasound. If the placenta still covers the endocervical os after 28 weeks, placenta praevia will be diagnosed and treated according to the principles of placenta praevia. If the pregnancy is <37 weeks, the fetus is alive, the pregnant woman is in good condition, and the amount of vaginal bleeding is small, there is no need for emergency delivery, and expectant therapy is feasible, so as to prolong the gestation weeks as much as possible and improve the survival rate of the fetus. If the bleeding is recurrent or heavy, it is necessary to consult a doctor as soon as possible and take appropriate treatment, including suppressing contractions, controlling bleeding, correcting anemia and preventing infection. In addition, pregnant women should take rest, avoid exertion and avoid sexual intercourse during pregnancy. If placenta praevia is diagnosed, absolute bed rest should be taken to prevent bleeding caused by activities, and if there is any discomfort, go to the hospital promptly.