Aspirin in Pregnancy: Lowering Preeclampsia Risk | High-Risk Pregnancies
New guidance from medical organizations is reinforcing the importance of low-dose aspirin for pregnant individuals at risk of preeclampsia, a potentially dangerous pregnancy complication. Whereas previous recommendations suggested initiating aspirin therapy before 16 weeks gestation for optimal effectiveness, current clinical practice continues to emphasize early identification of risk factors and subsequent aspirin prophylaxis.
Preeclampsia, characterized by high blood pressure and signs of organ damage, affects approximately 5% of pregnancies globally and remains a leading cause of maternal and fetal morbidity and mortality. The American College of Obstetricians and Gynecologists (ACOG), along with the Society for Maternal-Fetal Medicine (SMFM), and the U.S. Preventive Services Task Force (USPSTF) have long advocated for low-dose aspirin (81 mg daily) as a preventative measure, particularly for those identified as high-risk.
Updated recommendations from the USPSTF in September 2021 largely maintained the existing guidance, continuing to recommend low-dose aspirin for individuals with a high risk of preeclampsia based on medical history. But, the USPSTF likewise provided updated guidance regarding moderate-risk factors, now recommending low-dose aspirin for individuals with more than one moderate-risk factor. ACOG and SMFM continue to recommend initiating low-dose aspirin between 12 and 28 weeks of gestation, with an optimal window before 16 weeks.
Research indicates that the timing of initiation may impact efficacy. Studies suggest that initiating low-dose aspirin after 16 weeks’ gestation may not be as effective in reducing the risk of preeclampsia, severe preeclampsia, and fetal growth restriction. This underscores the require for early risk assessment during prenatal care.
Low-dose aspirin works by inhibiting cyclooxygenase enzymes, which helps to restore the balance between thromboxane A₂ and prostacyclin, reducing platelet aggregation and improving blood flow to the placenta. While generally well-tolerated, the use of aspirin in pregnancy requires careful consideration and should be determined in consultation with a healthcare provider.
The appropriate dosage of low-dose aspirin is generally considered to be 81 mg daily in the United States, although some research explores the potential benefits of 150 mg doses. Regular strength aspirin is not recommended as a pain reliever during pregnancy.
A comprehensive review published in November 2025 further supports the use of low-dose aspirin, noting that daily doses between 60 and 150 mg, initiated before 16 weeks of gestation, can significantly reduce the incidence of preterm and early-onset preeclampsia, as well as associated complications like fetal growth restriction and preterm delivery.
Despite the established benefits, ongoing research continues to refine understanding of optimal aspirin dosage and timing. As of February 16, 2026, no further updates to the USPSTF or ACOG/SMFM guidelines have been issued regarding the use of aspirin in preeclampsia prevention.