The association between aspirin use during pregnancy and risk for postpartum hemorrhage remains unclear. We aimed to explore the incidence of postpartum hemorrhage and the amount of postpartum blood loss among women who used aspirin during pregnancy.From inception through October 2021, we explored MEDLINE, Web of Science, Embase and Cochrane Central Register of Controlled Trials.Studies comparing pregnancy outcomes which covered the incidence of postpartum hemorrhage or amount of postpartum blood loss in pregnancies with aspirin versus placebo (or no aspirin) were included.Reviewers separately ascertained studies, obtained data, and gauged study quality. Meta-analysis was conducted by random effects model owing to the probable heterogeneity of included studies. The rate of postpartum hemorrhage or the mean amount of postpartum blood loss were compared and odds ratios (ORs) or mean differences (MDs) with 95% confidence intervals (CIs) were estimated. Two parts performed both a pooled analysis of RCTs and cohort studies and a separate analysis of RCTs.Overall, 21 studies with 373,926 women were included in postpartum hemorrhage part and 7 studies with 10,163 women were included in postpartum blood loss part. The results suggested that aspirin use during pregnancy was associated with increased incidence of postpartum hemorrhage (OR=1.20, 95% CI: 1.07 to 1.34). When only RCTs were retained, the results remained significant (OR=1.12, 95% CI: 1.00 to 1.25). In second part, higher total blood loss after delivery was obtained (MD: 12.85 ml, 95% CI: 3.28 to 22.42) and the result was unaltered when cohort studies were eliminated (MD:13.72 ml, 95% CI: 4.63 ml to 22.81 ml). The conclusions are more likely to be obtained in developed country.Aspirin use during pregnancy is a potential risk for postpartum hemorrhage and do slightly increase the amount of postpartum blood loss. Without denying the combined value of aspirin, our conclusions raise alarm for clinicians to postpartum hemorrhage in women using aspirin during pregnancy.Copyright © 2023 Elsevier Inc. All rights reserved.