中文摘要：

This prospective study was conducted to assess the rate of resolution of second trimester placenta previa in women with anterior placenta and posterior placenta, and that in women with and without previous cesarean section. In this study, placenta previa was defined as a placenta lying within 20 mm of the internal cervical os or overlapping it. We recruited 183 women diagnosed with previa between 20＋0 weeks and 25＋6 weeks. They were grouped according to their placenta location（anterior or posterior） and history of cesarean section. Comparative analysis was performed on demographic data, resolution rate of previa and pregnancy outcomes between anterior group and posterior group, and on those between cesarean section group and non-cesarean section group. Women with an anterior placenta tended to be advanced in parity（P=0.040） and have increased number of dilatation and curettage（P=0.044）. The women in cesarean section group were significantly older（P=0.000） and had more parity（P=0.000）, gravidity（P=0.000）, and dilatation and curettage（P=0.048） than in non-cesarean section group. Resolution of previa at delivery occurred in 87.43% women in this study. Women with a posterior placenta had a higher rate of resolution（P=0.030）, while history of cesarean section made no difference. Gestational age at resolution was earlier in posterior group（P=0.002） and non-cesarean section group（P=0.008） than in anterior group and cesarean section group correspondingly. Placenta location and prior cesarean section did not influence obstetric outcomes and neonatal outcomes. This study indicates that it is more likely to have subsequent resolution of the previa when the placenta is posteriorly located for women who are diagnosed with placenta previa in the second trimester.