Around the third month of pregnancy, if the placenta and the endocervical opening of the pregnant woman are relatively close to each other, it is considered to be a low lying placenta. The more common causes of hypoplastic placenta, there are endometrial factors, if usually have endometrial inflammation, endometrial injury, it is easy to lead to hypoplastic placenta. However, most of this kind of low lying placenta is temporary, and in the later stage, as the uterus continues to grow, the lower part of the uterus continues to lengthen, and the placenta’s position will slowly grow upwards. In most of the pregnant women, after 28 weeks, the placenta will be more than 70mm away from the cervical opening, which is a normal distance. If the placenta is still low after 28 weeks, it belongs to placenta praevia, and some of them are placenta praevia.