To examine the efficacy of preoperative prophylactic balloon occlusion (PPBO) of the internal iliac arteries (IIA) in women with placenta accrete spectrum (PAS) and placenta previa in reducing operative bleeding. MEDLINE, EMBASE, Web-of-Sciences, Scopus, the Cochrane Library, and ClinicalTrials.gov were searched from inceptions to March 2022 without language restriction. Search terms were as follows:[“Placenta accrete” OR “placenta increta” OR “placenta percreta” OR “placental abnormalities” OR “placenta accreta spectrum” OR “PAS” OR “placental diseases” OR “abnormal placentation” OR “Placenta Previa”] AND [“prophylactic” OR “balloon” OR “catheter” OR “occlusion” OR “endovascular” OR “iliac artery” OR “uterine artery” OR “interventional radiology”] AND [“randomized control study” OR “RCT” OR “controlled clinical trial” OR “Randomized controlled trial”]. Only peer-reviewed trials that compared the use of PPBO of the IIA compared to no use were included. The studies’ quality was assessed by the Cochrane Risk of Bias tool. Primary outcome was number of packed red blood cell (RBC) units transfused. Secondary outcomes included intra- and postoperative complications. The study was conducted according to a prospectively prepared protocol, registered with PROSPERO under CRD42016024244. Of 164 reports identified, 3 randomized trials representing 167 women (83 and 84 in the intervention and control groups, respectively) were eligible. All were judged to be at a low risk of bias. Mean number of packed RBC units transfused was 4.52±1.70 and 3.70±1.88 in the intervention and control groups, respectively (p=0.001), (Figure 1). Total operating time was significantly higher in the intervention group, (p=0.001) as well as the rate of postoperative fever (p=0.02). Transfusion of additional blood products, and other intra- and postpartum outcomes were comparable (Table 1). Use of PPBO of the IIA in PAS and placenta previa was associated with increased number of packed RBC units transfused, operating time and fever. Other pre- and postoperative outcomes were similar to the controls.View Large Image Figure ViewerDownload Hi-res image Download (PPT)