A randomized, double-blind, placebo-controlled trial evaluated the effectiveness of low-dose aspirin (150 mg/day) in reducing the risk of preterm preeclampsia in pregnancies at high risk. The study enrolled 1776 women with singleton pregnancies at high risk for preterm preeclampsia, who were randomly assigned to receive aspirin or placebo from 11 to 14 weeks of gestation until 36 weeks. The primary outcome was delivery with preeclampsia before 37 weeks of gestation. The results showed that aspirin reduced the incidence of preterm preeclampsia by 64% compared to placebo (1.6% vs. 4.3%). The study found no significant differences in neonatal adverse outcomes or other adverse events between the groups. Adherence to the treatment was high, with 79.9% of participants taking at least 85% of the prescribed tablets. The trial was not powered to detect differences in secondary outcomes. The study was supported by the European Union Seventh Framework Program and the Fetal Medicine Foundation. The findings suggest that low-dose aspirin is effective in reducing the risk of preterm preeclampsia in high-risk pregnancies. The study highlights the importance of early identification of high-risk pregnancies and the potential benefits of aspirin in preventing preterm preeclampsia. The results support the use of aspirin in high-risk pregnancies, particularly when initiated at 11-14 weeks of gestation. The study also emphasizes the need for improved screening methods to identify high-risk pregnancies accurately.A randomized, double-blind, placebo-controlled trial evaluated the effectiveness of low-dose aspirin (150 mg/day) in reducing the risk of preterm preeclampsia in pregnancies at high risk. The study enrolled 1776 women with singleton pregnancies at high risk for preterm preeclampsia, who were randomly assigned to receive aspirin or placebo from 11 to 14 weeks of gestation until 36 weeks. The primary outcome was delivery with preeclampsia before 37 weeks of gestation. The results showed that aspirin reduced the incidence of preterm preeclampsia by 64% compared to placebo (1.6% vs. 4.3%). The study found no significant differences in neonatal adverse outcomes or other adverse events between the groups. Adherence to the treatment was high, with 79.9% of participants taking at least 85% of the prescribed tablets. The trial was not powered to detect differences in secondary outcomes. The study was supported by the European Union Seventh Framework Program and the Fetal Medicine Foundation. The findings suggest that low-dose aspirin is effective in reducing the risk of preterm preeclampsia in high-risk pregnancies. The study highlights the importance of early identification of high-risk pregnancies and the potential benefits of aspirin in preventing preterm preeclampsia. The results support the use of aspirin in high-risk pregnancies, particularly when initiated at 11-14 weeks of gestation. The study also emphasizes the need for improved screening methods to identify high-risk pregnancies accurately.