由前置胎盘所致的大出血属于产科急症,如处理不当,危及母儿生命安全。正确识别并及早处理前置胎盘大出血,对降低孕产妇和围产儿死亡率均有重要意义。阴道大出血一般由完全性前置胎盘所致,常发生在30孕周以前,且反复发作。有时一次大出血则使孕妇陷入休克,使胎儿缺氧窘迫而死亡。在处理之前对前置胎盘作出确切分类,是正确制定处理方案的重要一环。B超对胎盘定位的准确率达95％,应列为 Bleeding caused by the placenta previa are obstetric emergencies, such as improper handling, endanger the safety of mother and child. Correct identification and early treatment of placenta previa bleeding, reduce maternal and perinatal mortality are of great significance. Vaginal bleeding is generally caused by the complete placenta previa, often occurs before the 30 gestational weeks, and recurrent. Sometimes a bleeding is pregnant women into shock, so that the fetus died of hypoxia. The exact classification of the placenta previa prior to treatment is an important part of developing a proper treatment plan. B ultrasound positioning accuracy of the placenta of 95%, should be classified as