Aspirin use during pregnancy and the risk of bleeding complications: A Swedish population-based cohort study.

Abstract Background Aspirin is offered to pregnant women to prevent preeclampsia, a severe obstetric complication. Large studies of non-pregnant populations have consistently shown aspirin prophylaxis increases the risk of hemorrhagic complications. However, there have not been any population-based studies investigating this in a pregnant population. Objective To investigate whether aspirin use during pregnancy is associated with an increased risk of bleeding complications. Study design We performed a register-based cohort study, using the Swedish Pregnancy Register where we examined 313,624 women giving birth between January 2013 – July 2017. Logistic regression was used to assess the risk of antepartum, intrapartum and postpartum hemorrhage. A propensity score and inverse probability treatment weighting was used to generate an odds ratio that corrects for differences in baseline characteristics. Results Aspirin use was registered in 4,088 (1.3%) of women during pregnancy. Compared to women who did not take aspirin, aspirin use was not associated with bleeding complications during the antepartum period [adjusted Odds Ratio (aOR) 1.22 (95% confidence interval (CI) 0.97, 1.54)]. However, aspirin users had a higher incidence of intrapartum bleeding (2.9% aspirin users vs 1.5% non-users: aOR 1.63 [95% CI 1.30, 2.05]), postpartum hemorrhage (10.2% vs 7.8%; aOR 1.23 [95% CI 1.08, 1.39]) and postpartum hematoma (0.4% vs 0.1%; aOR 2.21 [95% CI 1.13, 4.34]). The risk of a neonatal intracranial hemorrhage was also increased (0.07% vs 0.01%; aOR 9.66 [95% CI 1.88, 49.48]). After stratifying by mode of birth, the higher incidence of bleeding among aspirin users was present for those who had a vaginal birth but not those who had a caesarean section. Conclusion Using aspirin during pregnancy is associated with increased postpartum bleeding and postpartum hematoma. It may also be associated with neonatal intracranial hemorrhage. When offering aspirin during pregnancy these risks need to be weighed against the potential benefits.