A $0.03 Pill That Could Save Mothers' Lives: An Update on the State of Low-Dose Aspirin for Preeclampsia Prevention- part 2

These posts on aspirin and preeclampsia are not to be interpreted as medical advice.  Rather, they summarize the latest research on this subject.

Debate around dosage

A growing body of evidence now suggests that the standard U.S. dose of 81mg may be less than optimal. The landmark ASPRE trial, the largest prospective study to date, used 150mg/day and found a dramatic reduction in preterm preeclampsia. Multiple meta-analyses have since concluded that doses in the 150–162mg range are associated with significantly lower rates of preterm preeclampsia compared to 75–81mg, particularly for preterm disease.

A 2024 U.S. retrospective cohort study found that women taking 162mg (two standard 81mg tablets) had significantly lower rates of preeclampsia than those on 81mg or no aspirin at all, while bleeding rates were similar across groups. This has driven a new prospective randomized trial, the 2025 ASAPP trial, which is now comparing 81mg LDA versus 162mg LDA in the United States to settle the dose question. The 81mg standard currently recommended in the U.S. may not be enough, especially for preventing the most severe and preterm forms of preeclampsia.

Timing is critical

To be effective against pre-eclampsia, aspirin must be started before 16 weeks of gestation. A review of 45 randomized trials confirmed significant reductions in preeclampsia, severe preeclampsia, and fetal growth restriction when aspirin was initiated before 16 weeks, with much weaker or no effect when started later. Ideally, initiation between 11 and 14 weeks appears to offer the most benefit.
Research shows that taking LDA at bedtime outperforms taking LDA in the morning, afternoon, or evening, most likely due to circadian patterns and metabolism.

Is it safe?

A 2024 study on children whose mothers participated in aspirin trials found no worsening of cognitive development in children aged 33–39 months following prenatal aspirin exposure. The Preeclampsia Foundation continues to track longer-term child outcomes, and the data remains reassuring. Postpartum hemorrhage, a major medical concern, has not been found in large U.S. trials at doses of 81–162mg, although this remains an active area of monitoring, especially in low- and middle-income countries.

Post by Brittany de Soto Palmer