(1185) Aspirin Dose and Risk of Postpartum Hemorrhage: A Retrospective Cohort Study

To evaluate whether aspirin at 81 mg or 162 mg daily, compared to no aspirin, is associated with postpartum hemorrhage (PPH) and total blood loss (TBL) in patients receiving aspirin for preeclampsia prevention. 

Study Design:

This retrospective cohort analysis included 30,941 singleton pregnancies delivered ≥ 24 weeks at a single academic tertiary care center 2015 - 2024. Patients were analyzed by aspirin exposure: no aspirin, 81 mg, or 162 mg daily, initiated between 12-28 weeks. The primary outcome was PPH (blood loss ≥ 1000 mL); secondary outcome was TBL, stratified by mode of delivery. Multivariate logistic and linear regression models adjusting for race, BMI, magnesium sulfate, anticoagulation use, and delivery year to account for prescribing trends were developed. 

Results:

PPH occurred in 27.1% of the no aspirin, 19.2% in the 81 mg, and 15.8% in the 162 mg groups respectively (p< 0.001). Adjusted odds of PPH were significantly lower in aspirin groups compared to no aspirin (81 mg: aOR 0.836, CI 0.725-0.965; 162 mg: aOR 0.779, CI 0.670-0.960). Stratified analysis showed this effect was limited to vaginal deliveries, where both doses were associated with ~53% lower odds of PPH (81 mg: aOR 0.462, CI 0.351-0.608; 162 mg: aOR 0.469, CI 0.353-0.623). Among cesarean deliveries, no significant association was found (81 mg: aOR 1.17, CI 0.97-1.40; 162 mg: aOR 0.92, CI 0.75-1.12). Linear regression showed significantly lower TBL in aspirin groups among vaginal births (p< 0.001), but not among cesarean or operative vaginal births. 

Conclusion:

Both aspirin doses were associated with reduced PPH risk and lower TBL among vaginal deliveries. This could be due to aspirin’s anti-inflammatory effects, which may mitigate bleeding risk during labor, where inflammation plays a greater role. This protective effect did not extend to cesarean births, where hemorrhage is likely more affected by surgical factors. Regardless, these findings support the safety of aspirin at both 81 mg and 162 mg and may guide dose selection for preeclampsia prevention.