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Can Low-Dose Aspirin During Pregnancy Prevent Preeclampsia?

prevent preeclampsia

Preterm preeclampsia is a major cause of maternal and neonatal complications and death. Researchers investigated the benefit of low-dose aspirin during pregnancy to prevent preeclampsia in high-risk pregnant women.

Preeclampsia is a serious condition that can lead to complications and death for the mother and baby, with a higher risk if it’s early in onset and severe, which can result in preterm delivery at less than 37 weeks gestation. Over the years, there have been many trials that evaluated the benefits of low-dose aspirin, at varying dosages and gestational ages, in preventing preeclampsia. However, as there continues to be uncertainty surrounding the use of aspirin during pregnancy to prevent preeclampsia, researchers designed a trial to evaluate aspirin’s benefit in preventing this condition.

In a study published in The New England Journal of Medicine, researchers in the UK tested their hypothesis that low-dose aspirin taken from 11 to 14 weeks of gestation until 36 weeks of gestation in high-risk women would result in half the incidence of preterm preeclampsia compared to placebo. In this multicentre, double-blinded trial, eligible women were randomly assigned to receive either 150 mg aspirin or a placebo—which were manufactured to be identical in appearance, size and shape—and instructed to take one tablet every night until 36 weeks of gestation or at the onset of labour (in the case of early delivery).

The study’s primary outcome was preeclampsia delivery before 37 weeks of gestation, with secondary outcomes being adverse events before, at, or after 37 weeks of gestation, stillbirth, neonatal death or complications, and poor fetal growth. Follow-up clinic visits and telephone interviews were performed throughout the pregnancy to assess for adverse events and adherence.

A total of 1,620 women participated in the trial; with 798 women in the aspirin group and 822 women in the placebo group. The baseline characteristics between the aspirin and placebo group were similar as there were no significant differences between the two. In the aspirin group, preeclampsia occurred in 1.6% of women, while in the placebo group, preeclampsia occurred in 4.3% of women. With regards to adherence and other adverse outcomes measured, there was no significant difference observed between the two groups in both categories.

The study’s findings show that low-dose aspirin in pregnant women who are at high risk for preterm preeclampsia results in a reduced incidence of preeclampsia compared to placebo. Decisions regarding the study’s methods were made based on previous evidence suggestive of the most effective aspirin dosage and administration. A greater benefit to prevent preeclampsia is conferred if aspirin is started at or before 16 weeks of gestation and is most effective at a dose of 150 mg.

The screening algorithm the study used to assess for women at high risk of preterm preeclampsia has been shown to be superior to other currently used methods, as it combined the screening of a number of different maternal characteristics, factors and biomarkers. Overall, in pregnant women identified as high risk for preterm preeclampsia, treatment with 150 mg of aspirin daily from 11 to 14 weeks of gestation until 36 weeks of gestation led to a significant reduction in the incidence of preterm preeclampsia when compared to a placebo.

Written by Maggie Leung, PharmD


Rolnik, D. L., Wright, D., Poon, L. C., O’Gorman, N., Syngelaki, A., Matallana, C. D., . . . Nicolaides, K. H. (2017). Aspirin versus Placebo in Pregnancies at High Risk for Preterm Preeclampsia. New England Journal of Medicine, 377(7), 613-622. doi:10.1056/nejmoa1704559

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