Abstract: 【Abstract】 Objective To investigate the severe adverse pregnancy outcomes in pregnancies with placenta previa and prior cesarean delivery and its risk factors. Methods This retrospective casecontrol study reviewed all pregnancies with placenta previa and prior cesarean delivery delivered by repeat cesarean section in our institution between January 2005 and June 2015, and investigated the incidence of severe adverse pregnancy outcome. A composite of severe adverse pregnancy outcomes (including transfusion of 10 units or more red blood cells, maternal ICU admission, unanticipated injuries, repeat operation, hysterectomy, and maternal death) and other maternal and neonatal outcomes were described. Univariate and multivariable logistic regression analysis were used to quantify the effects of risk factors on severe adverse pregnancy outcomes. Results There were 478 women with placenta previa and prior cesarean delivery in our hospital over the last decade. The average age of them was 32.5±4.8 years old, most women were beyond 30 years old, the average gravidity and parity were 4 and 1, 131 cases (27.4%) had severe adverse pregnancy outcomes. Transfusion of 10 units or more red blood cells happened in 75 cases (15.7%, 75/478); 44 cases (9.2%, 44/478) necessitated maternal ICU admission; unanticipated bladder injury occurred in 11 cases, but non ureter or bowel injury happened; All 4 repeat operations were due to delayed hemorrhage after conservative management during cesarean delivery, and an emergent hysterectomy was performed for all of the 4 cases. Hysterectomy (107 cases, 22.4%) was the most common severe adverse pregnancy outcome. Among all 311 morbidly adherent placenta cases finally confirmed by pathological or surgical findings or both, only 172 (55.3%) were suspected before delivery. Multivariable logistic regression analysis showed that the risk of severe adverse