Background: Although low-dose aspirin has been reported to reduce the incidence of preeclampsia among women at high risk for this complication, its efficacy and safety in healthy, nulliparous pregnant women are not known.
Methods: We studied 3135 normotensive nulliparous women who were 13 to 26 weeks pregnant to determine whether treatment with aspirin reduced the incidence of preeclampsia. Of this group, 1570 women received 60 mg of aspirin per day and 1565 received placebo for the remainder of their pregnancies. We also evaluated the effect of aspirin on maternal and neonatal morbidity.
Results: Of the original group of 3135 women, 2985 (95 percent) were followed throughout pregnancy and the immediate puerperium. The incidence of preeclampsia was lower in the aspirin group (69 of 1485 women [4.6 percent]) than in the placebo group (94 of 1500 women [6.3 percent]) (relative risk, 0.7; 95 percent confidence interval, 0.6 to 1.0; P = 0.05), whereas the incidence of gestational hypertension was 6.7 and 5.9 percent, respectively. There were no significant differences in the infants' birth weight or in the incidence of fetal growth retardation, postpartum hemorrhage, or neonatal bleeding problems between the two groups. Subgroup analysis showed that preeclampsia occurred primarily in women whose initial systolic blood pressure was 120 to 134 mm Hg (incidence among such women, 5.6 percent in the aspirin group vs. 11.9 percent in the placebo group; P = 0.01). The incidence of abruptio placentae was greater among the women who received aspirin (11 women, vs. 2 in the placebo group; P = 0.01).
Conclusions: Low-dose aspirin decreases the incidence of preeclampsia among nulliparous women, primarily through its effect in those who have elevated systolic blood pressure initially. This treatment does not decrease perinatal morbidity but increases the risk of abruptio placentae.