妊娠28周后,胎盘附着于子宫下段,甚至胎盘下缘达到或覆盖宫颈内口,其位置低于胎先露部,称为前置胎盘(placenta previa,PP)。近年其发病率呈上升趋势,并仍然是严重威胁母儿安全的妊娠晚期严重并发症之一。1高危因素1·1高龄孕妇年龄35岁,发病率增加。1·2流产史或前次剖宫产史N After 28 weeks of gestation, the placenta is attached to the lower part of the uterus, and even the lower edge of the placenta reaches or covers the mouth of the cervix, which is lower than the anterior part of the fetus and is called the placenta previa (PP). Its incidence has been on the rise in recent years and remains one of the serious complications of late pregnancy in a serious threat to mother-child safety. 1 risk factors 1.1 older pregnant women aged 35 years old, the incidence increased. Abortion history or previous cesarean section history