Low-Dose Aspirin is Not Associated with Increased Risk of Postpartum Hemorrhage

Aspirin (ASA) is recommended for preeclampsia prophylaxis, but it is uncertain whether higher doses, such as the 150 mg/day used in the ASPRE trial, increase the risk of postpartum hemorrhage (PPH). In Canada, the available formulation is 81 mg/day. We hypothesized that ASA 162 mg/day may increase the risk of PPH and other bleeding complications. We aimed to evaluate whether ASA 162 mg/day for preeclampsia prevention is associated with increased risk of PPH or other maternal or neonatal bleeding events.

This retrospective cohort study included patients taking ASA 162 mg/day between 12-36 weeks gestation for preeclampsia prophylaxis and delivered between January 2020 and January 2023. A low-risk group not receiving ASA served as controls. Exclusion criteria included anticoagulant use, uterine anomalies, and placenta previa/accreta spectrum. The primary outcome was PPH, defined as the use of blood transfusion, additional uterotonics or tranexamic acid, hemostatic surgery, or tamponade. Secondary outcomes included composite maternal bleeding. Propensity score matching was performed, and outcomes were stratified by mode of delivery.

After matching, 882 patients remained (223 ASA; 659 controls). There was no significant difference in PPH between ASA and controls (12.1% vs. 7.0%, P = 0.12; OR 1.84; 95% CI 0.84-4.03). Risk was not different in cesarean deliveries (8.3% vs. 9.6%, P = 0.44). Composite maternal hemorrhage did not differ significantly (65.5% vs. 63.4%, P = 0.58). A non-significant difference in PPH was noted in cesarean births (adjusted OR 1.80; 95% CI 0.99-3.27).

ASA 162 mg/day for preeclampsia prophylaxis was not associated with increased risk of PPH or other bleeding complications.