Why is aspirin (acetylsalicylic acid) given for high-risk preeclampsia?

From the Guidelines

Aspirin is recommended for high-risk eclampsia prevention because it reduces the risk of developing this serious pregnancy complication. The use of low-dose aspirin for the prevention of morbidity and mortality from preeclampsia is supported by the U.S. Preventive Services Task Force recommendation statement 1.

Key Points

• Low-dose aspirin (60-80 mg daily) should be started during the late first trimester, as early as 12 weeks of gestation, and continued until delivery.
• The typical regimen is 75-81 mg (one baby aspirin) taken daily, with some guidelines specifying 60-80 mg/d 1.
• This intervention is specifically indicated for women with risk factors such as previous preeclampsia, chronic hypertension, multifetal pregnancy, type 1 or 2 diabetes, renal disease, or autoimmune disorders.
• Aspirin works by inhibiting thromboxane production while preserving prostacyclin, which improves the balance between these compounds and promotes better placental development and blood flow, helping to prevent the placental dysfunction that underlies preeclampsia.
• The safety profile of low-dose aspirin in pregnancy is excellent, with minimal risks of maternal or fetal complications, as noted by various organizations including the American Congress of Obstetricians and Gynecologists, the World Health Organization, and the National Institute for Health and Care Excellence 1.

Administration

• The medication should be taken at a consistent time, with some guidelines suggesting nighttime administration due to the circadian variation in platelet activity.
• It is essential to follow the recommended dosage and administration schedule to maximize the benefits of aspirin in preventing high-risk eclampsia while minimizing potential risks.

From the Research

Aspirin for High-Risk Eclampsia

• Aspirin is given to pregnant women at high risk of preeclampsia to reduce the risk of developing the condition 2, 3, 4, 5, 6.
• The American College of Obstetricians and Gynecologists recommends initiation of 81 mg of aspirin daily for women at risk of preeclampsia between 12 and 28 weeks' gestation 2.
• The US Preventive Services Task Force recommends the use of low-dose aspirin (81 mg/d) as preventive medication for preeclampsia after 12 weeks of gestation in persons who are at high risk for preeclampsia 3.
• A daily dosage of 150 mg of aspirin, initiated before 16 weeks of gestational age, has been shown to reduce the incidence of preterm preeclampsia by 62% 4.
• Aspirin use is associated with lower risk of preeclampsia, perinatal mortality, preterm birth, and intrauterine growth restriction, without evident harms 6.

Dosage and Timing

• The optimal dosage of low-dose aspirin for preeclampsia prophylaxis is still a subject of debate, with some studies suggesting 81 mg and others suggesting 150 mg or higher 2, 4, 5.
• The timing of aspirin initiation is also important, with most studies suggesting initiation before 16 weeks of gestation 2, 3, 4.
• Doses of >100 mg of aspirin daily initiated before 16 weeks' gestation seem to be most effective at reducing the risk of preeclampsia 2.

Benefits and Harms

• Aspirin use is associated with lower risks of serious perinatal outcomes for individuals at increased risk for preeclampsia, without evident harms 3, 6.
• The absolute risk reductions for preeclampsia associated with aspirin use ranged from -1% to -6% across larger trials 6.
• There were no significant associations of aspirin use with risk of postpartum hemorrhage or other bleeding-related harms 6.