胎盘在正常情况下附着于子宫体部的后壁、前壁或侧壁。孕 2 8ｗ后若胎盘附着于子宫下段 ,甚至胎盘下缘达到或覆盖宫颈内口 ,其位置低于先露部 ,称前置胎盘。前置胎盘是妊娠晚期出血的主要原因之一 ,是妊娠期的严重并发症 ,处理不当能危及母儿生命。其发生率 2 0世纪 6 0～ 80年 The placenta is attached to the posterior, anterior, or lateral walls of the uterine body under normal conditions. Pregnancy 2 8w after the placenta attached to the lower uterine segment, or even reach the lower edge of the placenta to cover the cervix within the mouth, its location below the first exposed part, said placenta previa. Placenta previa is one of the main reasons for bleeding in the third trimester of pregnancy is a serious complication of pregnancy, improper handling can endanger the lives of mothers and children. The incidence of 20 century 60 ~ 80 years