Preeclampsia is a serious complication of pregnancy that can cause the death of the mother and child. The risk of complications is higher when preeclampsia is severe and of early onset. Identifying women at high risk for preeclampsia and determining interventions to reduce its prevalence are priorities of modern obstetrics. One intervention currently recommended by professional associations is the prophylactic use of low-dose (60 to 80 mg/day) aspirin.

Researchers conducted a multicenter, double-blind, placebo-controlled trial to determine whether low-dose (150 mg/day) aspirin taken from 11 to 14 weeks' gestation until 36 weeks' gestation would lower the incidence of preterm preeclampsia in women at high risk for the condition. Of 26,941 women with singleton pregnancies who underwent screening, 2,641 were found to be at high risk for preterm preeclampsia and eligible for the trial. Of these, 1,776 women agreed to participate in the trial and were randomly assigned to receive aspirin or placebo.

Thirteen (1.6%) women in the aspirin group compared with 35 (4.3%) in the placebo group had preeclampsia before 37 weeks' gestation (adjusted odds ratio in the aspirin group, 0.38; 95% confidence interval, 0.20 to 0.74; P = 0.004), which was the primary outcome of the study. The size of the treatment effect was consistent across estimated risk groups at the time of screening, across groups defined according to obstetrical history, and across countries (hospitals in the United Kingdom, Spain, Italy, Belgium, Greece, and Israel participated in the study).

There were no significant differences in the incidence of secondary outcomes, including stillbirth or neonatal death, for those in the aspirin and placebo groups. However, the authors note that the trial wasn't powered for those outcomes. The incidence of adverse events was also similar in the two groups. Adherence to treatment was good, with 79.9% of women reporting that they took at least 85% of the required number of tablets.

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