Preeclampsia occurs in approximately 5% of pregnancies worldwide and is the second leading cause of maternal mortality, following postpartum hemorrhage. It is a serious pregnancy complication characterized by sudden onset or progression of high blood pressure after 20 weeks of gestation, along with proteinuria or dysfunction of maternal organs.
Strong clinical evidence suggests that low-dose aspirin is the only effective medication for preventing preeclampsia. However, the optimal dosage remains uncertain due to limited research. As a result, international guidelines vary significantly. Some recommend doses <100 mg (75-81 mg), while others support higher doses≥ 100 mg (150-162 mg). Aspirin use in pregnancy has also been associated with an elevated risk of bleeding.
Swedish national registers, like the Swedish Medical Birth Register, the Swedish Prescribed Drug Register, the National Patient Register, and the Sweden Statistics Education Register, offer comprehensive data on aspirin exposure at different doses and outcomes, such as bleeding complications and preeclampsia. This data was utilized to compare the effects of higher doses (150-160 mg) versus lower doses (75 mg) of aspirin during pregnancy, specifically examining their association with preeclampsia and bleeding complications. This Swedish cohort study was published in JAMA Network Open on February 3, 2025.
13,828 Swedish women (mean age = 33 ± 5.5 years, with 3,003 nulliparous women) who gave birth at 22 weeks or later from January 2017 to December 2020 were included. Pregnant women with a history of existing cardiovascular diseases were excluded. Among them, 33.9% (n = 4687) of women took high-dose aspirin (150-160 mg), while 66.1% (n = 9141) took low-dose aspirin (75 mg). Moreover, 76.9% of women had at least two dispensed prescriptions for low-dose aspirin.
This large-population study showed that preeclampsia was observed in 9.5% of the high-dose aspirin group compared to 8.9% of the low-dose aspirin group with a non-significant relative risk (RR) of 1.06 (95% confidence interval [CI], 0.95-1.19) and adjusted RR (aRR) of 1.07 (95% CI, 0.93-1.24). Full-term preeclampsia was reported in 6.7% of the high-dose aspirin group compared to 6.1% of the low-dose aspirin group with aRR of 0.96 (95% CI, 0.81-1.13). Additionally, no difference was observed between 53 patients in the high-dose aspirin group and 98 patients in the low-dose aspirin group in risk of occurring preeclampsia with small for gestational age infants (aRR, 1.45; 95% CI, 0.93-2.25).
Furthermore, postpartum hemorrhage occurred in 6.9% of the 150-160 mg aspirin group compared to 6.4% of the 75 mg of aspirin group with RR of 1.09 (95% CI, 0.96-1.25) and aRR of 1.08 (95% CI, 0.90-1.30). Likewise, 11.9% of participants using 150-160 mg of aspirin group were associated with an elevated risk of anemia diagnosis at birth compared to 8.6% of women using 75 mg of aspirin with aRR of 1.42 (95% CI, 1.24-1.62).
This study’s limitations include a lack of data on certain risk factors, such as the family history of preeclampsia and blood pressure measurements, which influence aspirin dosing. Hemorrhage during cesarean delivery was classified as occurring during surgery, not after birth; as a result, many cases were not recorded as postpartum hemorrhage.
In conclusion, the study found no difference in the incidence of preeclampsia and bleeding complications between high (150-160 mg) and low (75 mg) doses of aspirin for preeclampsia prevention. These findings highlight that either dose may be prescribed. However, large randomized clinical studies are still needed to assess the optimal dose of aspirin during pregnancy.
Reference: Kupka E, Hesselman S, Gunnarsdóttir J, et al. Prophylactic Aspirin Dose and Preeclampsia. JAMA Netw Open. 2025;8(2):e2457828. doi:10.1001/jamanetworkopen.2024.57828
