Abstract： Objective:To study the risk factors of adverse pregnancy outcomes for induced abortion of cesarean scar pregnancy in midtrimester.Methods:A national multicenter retrospective study was conducted. A total of 154 singletons pregnant women with cesarean scar pregnancy during the second trimester induced abortion by various reasons in 12 tertiary A hospitals were selected, their pregnant outcomes were observed and the risk factors of serious adverse outcomes were analyzed with univariate and multivariate logstic regression; the role of ultrasound and MRI in predicting placenta accreta and severe adverse outcomes was evaluated, the effectiveness of uterine artery embolization (UAE) in preventing hemorrhage in pregnant women with and without placenta accreta was compared.Results:Among 154 subjects, the rate of placenta accreta was 42.2% (65/154), the rate of postpartum hemorrhage≥1 000 ml was 39.0% (60/154), the rate of hysterectomy was 14.9% (23/154), the rate of uterine rupture was 0.6% (1/154). The risk factor of postpartum hemorrhage≥1 000 ml and hysterectomy was placenta accreta ( P<0.01). For each increase in the number of parity, the risk of placenta accreta increased 2.385 times (95% CI: 1.046-5.439; P=0.039); and the risk of placenta accreta decreased with increasing ultrasound measurement of scar myometrium thickness ( OR=0.033, 95% CI: 0.001-0.762; P=0.033). The amount of postpartum hemorrhage and hysterectomy rate in the group with placenta accreta diagnosed by ultrasound combined with MRI were not significantly different from those in the group with placenta accreta diagnosed by ultrasound only or MRI only (all P>0.05). For pregnant women with placenta accreta, there were no significant difference in the amount of bleeding and hysterectomy rate between the UAE group [median: 1 300 ml; 34% (16/47)] and the non-embolization group (all P>0.05); in pregnant women without placenta accreta, the amount of bleeding in the UAE group was lower than that in the non-embolization group (median: 100 vs 600 ml; P<0.01), but there was no significant difference in hysterectomy rate [2% (1/56) vs 9% (3/33); P>0.05]. Conclusions:(1) Placenta accreta is the only risk factor of postpartum hemorrhage≥1 000 ml with hysterectomy for induced abortion of cesarean scar pregnancy in midtrimester; multi-parity and ultrasound measurement of scar myometrium thickness are risk factors for placenta accreta. (2) The technique of using ultrasound and MRI in predicting placenta accreta of cesarean scar pregnancy needs to be improved. (3) It is necessary to discuss of UAE in preventing postpartum hemorrhage for induced abortion of cesarean scar pregnancy in midtrimester.