Physicians from 213 centers in sixteen countries between January 1988 and December 1992 enrolled 9364 pregnant women between 12-32 weeks of gestation who were at high risk of developing preeclampsia or intrauterine growth retardation to determine whether the daily consumption of a 60 mg dose of aspirin would have any preventive effect against pregnancy-related hypertension (preeclampsia) or treat its symptoms. Subjects had an history of hypertension during pregnancy or intrauterine growth retardation. Among all study participants 74% were enrolled to prevent preeclampsia 12% to treat preeclampsia 12% to prevent intrauterine growth retardation and 3% to treat intrauterine growth retardation. 4659 women took aspirin tablets daily while the remaining 4650 consumed placebos. Investigators then looked at the birth outcomes among women in each respective group. Overall 7% of the women who took aspirin daily developed proteinuric preeclampsia compared with 8% of the women who took the placebo. Seven women in each group (0.2%) progressed to eclampsia (convulsions). The difference in results between groups was not statistically significant. Taking an aspirin per day from the second trimester of pregnancy through delivery therefore does little to prevent preeclampsia or treat its symptoms. A daily dose of aspirin also appears to have little or no discernible effect upon the risk of intrauterine growth retardation. The one discernible effect of daily aspirin use was a significant trend toward a greater reduction in preeclampsia which occurs early in pregnancy.