OC19.06: Prevalence of postpartum hemorrhage in patients on ASA 162mg/day for pre‐eclamspia prevention

To assess the risk of postpartum hemorrhage (PPH) in patients on pre-eclampsia prophylactic ASA on the available recommended dose of 162mg/day. A retrospective observational study was conducted at The Ottawa Hospital from January 2020 to December 2022. We compared the incidence of PPH in patients on ASA 162mg/day started at any time before 16 weeks to controls not taking ASA. PPH was defined by use of any uterotonic agent other than the standard of care (oxytocin) and/or use of any intervention to control excessive bleeding (Bakri balloon, uterine artery ligation/embolization, hysterectomy). We used this as a surrogate for the definition of PPH as absolute blood loss estimation can be subjective. We analysed patients who had a vaginal delivery and Caesarean in 2 subgroups. We excluded patients with any risk factors for PPH, such as multiple gestation, therapeutic anticoagulation, fibroids, uterine anatomical anomalies, placenta previa, placenta accreta spectrum disorders, and hereditary coagulopathies. A multivariate logistic regression was performed to control for confounders such as fetal macrosomia, general anesthesia, multiparty, pre-eclampsia and chronic hypertension. N = 3855 patients (307 ASA vs 3548 control group) were compared. Overall, the prevalence of PPH was 66.4% in the ASA vs 61% in the control group (p = 0.058) Amongst patients who delivered vaginally, no differences were found for PPH between ASA and control (36.8% vs 44.5%, p = 0.09) and the difference was still not significant when adjusted. Similarly, no differences were found amongst patients who had a Caesarean (86.8% vs 85.6%, p = 0.65). Our results show the prevalence of PPH is not statistically different between patients taking 162mg/d of ASA and controls.