正常胎盘附着于子宫体部的前壁、后壁或侧壁。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处 ,其位置低于胎儿先露部 ,称为前置胎盘。前置胎盘是妊娠中晚期严重的并发症 ,并为妊娠中晚期阴道出血的最常见原因。往往起病急 ,进展快 ,可严重威胁母儿的生命。本文拟就 The normal placenta adheres to the anterior, posterior or lateral walls of the uterine body. If the placenta attached to the lower uterine segment, or even lower edge of the placenta to reach or cover the mouth of the cervix, its location lower than the fetal first exposed part, known as the placenta previa. Placenta previa is a serious complications in the second trimester of pregnancy, and the most common cause of vaginal bleeding in the second trimester. Often acute onset, rapid progress, can seriously threaten the lives of mothers and children. This article is intended