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

Background: Aspirin is offered to pregnant women to prevent preeclampsia, a severe obstetrical complication. Large studies of nonpregnant populations have consistently shown that aspirin prophylaxis increases the risk of hemorrhagic complications. However, there have not been any population-based studies investigating this in a pregnant population. Objective: This study aimed 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 wherein we examined 313,624 women giving birth between January 2013 and 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 4088 (1.3%) women during pregnancy. Compared with women who did not take aspirin, aspirin use was not associated with bleeding complications during the antepartum period (adjusted odds ratio, 1.22; 95% confidence interval, 0.97–1.54). However, aspirin users had a higher incidence of intrapartum bleeding (2.9% aspirin users vs 1.5% nonusers; adjusted odds ratio, 1.63; 95% confidence interval, 1.30–2.05), postpartum hemorrhage (10.2% vs 7.8%; adjusted odds ratio, 1.23; 95% confidence interval, 1.08–1.39), and postpartum hematoma (0.4% vs 0.1%; adjusted odds ratio, 2.21; 95% confidence interval, 1.13–4.34). The risk of a neonatal intracranial hemorrhage was also increased (0.07% vs 0.01%; adjusted odds ratio, 9.66; 95% confidence interval, 1.88–49.48). After stratifying by mode of birth, a higher incidence of bleeding among aspirin users was present for those who had a vaginal birth but not those who had a cesarean delivery. 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.