BackgroundRetained products of conception (RPOC) often cause severe postpartum hemorrhage (PPH) but the clinical significance of RPOC in placenta previa is unclear. This study aimed to investigate the clinical significance of RPOC in women with placenta previa. The primary outcome was to evaluate risk factors of RPOC and the secondary outcome was to consider risk factors of severe PPH.MethodsSingleton pregnant women with placenta previa who underwent cesarean section (CS) and placenta removal during the operation at the National Defense Medical College Hospital between January 2004 and December 2021 were identified. A retrospective analysis was performed to examine the frequency and risk factors of RPOC and the association of RPOC with severe PPH in pregnant women with placenta previa.ResultsThis study included 335 pregnant women. Among these, 24 (7.2%) pregnant women developed RPOC. Pregnant women with prior CS (Odds Ratio (OR) 5.98; 95% Confidence Interval (CI) 2.35–15.20,p< 0.01), major previa (OR 3.15; 95% CI 1.19–8.32,p< 0.01), and placenta accreta spectrum (PAS) (OR 92.7; 95% CI 18.39–467.22,p< 0.01) were more frequent in the RPOC group. Multivariate analysis revealed that prior CS (OR 10.70; 95% CI 3.47–33.00,p< 0.01,) and PAS (OR 140.32; 95% CI 23.84–825.79,p< 0.01) were risk factors for RPOC. In pregnant women who have placenta previa with RPOC or without RPOC, the ratio of severe PPH were 58.3% and 4.5%, respectively (p< 0.01). Furthermore, the occurrence of prior CS (OR 9.23; 95% CI 4.02–21.20,p< 0.01), major previa (OR 11.35; 95% CI 3.35–38.38,p< 0.01), placenta at the anterior wall (OR 3.44; 95% CI 1.40–8.44,p= 0.01), PAS (OR 16.47; 95% CI 4.66–58.26,p< 0.01), and RPOC (OR 29.70; 95% CI 11.23–78.55,p< 0.01) was more in pregnant women with severe PPH. In the multivariate analysis for severe PPH, prior CS (OR 4.71; 95% CI 1.29–17.13,p= 0.02), major previa (OR 7.50; 95% CI 1.98–28.43,p< 0.01), and RPOC (OR 13.26; 95% CI 3.61–48.63,p< 0.01) were identified as risk factors.ConclusionsPrior CS and PAS were identified as risk factors for RPOC in placenta previa and RPOC is closely associated with severe PPH. Therefore, a new strategy for RPOC in placenta previa is needed.Supplementary InformationThe online version contains supplementary material available at 10.1186/s12884-023-05805-0.