Abstract: 【ABSTRACT】Objective: To analyze in the middle and late pregnancy causes of hemorrhage,and to explore the influence pregnancy outcome in the mid and late gestation hemorrhage by prenatal ultrasound.Methods:From February were selected in late pregnancy pregnancy 129 cases of maternal hemorrhage in our hospital as the observation group.100 cases of normal pregnant women in our hospital during the same period of time were recorded as a control group.The incidence rate of the two groups was compared with the incidence of placenta and the causes of hemorrhage were determined,and the risk factors of placenta were further explored.At last,through the comparison of prenatal ultrasonography and CT diagnosis of hemorrhage during middle and late pregnancy,and statistical analysis of influence pregnancy outcome.Results:Main risk factors of placenta previa was age,educational level,history of abortion and cesarean section production history.The accuracy,sensitivity and specificity of prenatal ultrasound examination were significantly higher than that of routine CT examination,and the diagnostic rate of missed diagnosis was lower than that of CT.The proportion of cesarean section,premature delivery,fetal distress and neonatal asphyxia were significantly higher in the observation group than in control group.The difference was statistically significant(P＜0.05).Conclusion:The main cause of bleeding in late pregnancy is placenta previa,placental abruption,age,history of abortion,is caused by the risk factors of placenta previa.Prenatal ultrasound can effective detection of late pregnancy bleeding,have very high sensitivity and specificity.