Objective To investigate the risk factors,management and prophylaxis of dangerous placenta previa.Methods The clinical data of 407 cases of placenta previa were reviewed,36 cases of them with dangerous placenta previa.Comparison was made between group A (dangerous placenta previa,36 cases) and group B (non dangerous placenta previa,371 cases) in terms of age,number of pregnancy and number of ceasarean delivery.Results The incidence rates of pregnant women in group A age ≥ 35years,number of pregnancy ≥3times,and cesarean delivery≥2times were 55.6％,61.1％,25.0％,which were significantly higher than those of group B (25.6％,27.7％,2.4％),the differences were statistically significant (x2 =7.71,8.99,21.97,all P ＜ 0.01).Among the 36 cases of dangerous placenta previa,12 cases were diagnosed with concomitant placenta increta.The specificity and sensitivity for detection of placenta increta were 90.5％ (19/21) and 83.9％ (10/12) of ultrasonography respectively,and those were 100.0％ (3/3) and 87.5％ (7/8) of MRI.Of the 36 dangerous placenta previa patients,two patients were treated with induced labour due to unexpected pregnancy under 28 weeks,while the others were refer to surgical operation.5 surgical patients experienced uncontrollable postpartum haemorrhage which necessitated histectomy,while the other 31 cases received conservative operation.Rate of histectomy was 13.9(5/36).Conclusion Dangerous placenta previa is associated with advanced age,multiple pregnancy and multiple cesarean delivery.Accurate preoperational evaluation of the placenta previa should be acquired with ultrasonography and MRI to detect placenta increta,provide information for treatment selection,and prevent postpartum haemorrhage.