Low‐dose aspirin (LDA) has been proposed to improve pregnancy outcomes in couples experiencing recurrent pregnancy loss. However, results from studies of LDA on pregnancy outcomes have been inconsistent, perhaps because most studies evaluated LDA‐initiated post‐conception. The purpose of the Effects of Aspirin in Gestation and Reproduction (EAGeR) trial was to determine whether preconception‐initiated LDA improves livebirth rates in women with one to two prior losses.

We performed a multicentre, block randomised, double‐blind, placebo‐controlled trial. Study participants were recruited using community‐based advertisements and physician referral to four university medical centres in the US (2006–12). Eligible women were aged 18–40 years actively trying to conceive, with one to two prior losses. Participants were randomised to receive daily LDA (81 mg/day) or a matching placebo, and all were provided with daily 400‐mcg folic acid. Follow‐up continued for ≤6 menstrual cycles while attempting to conceive. For those who conceived, treatment was continued until 36 weeks gestation. The primary outcome was the cumulative livebirth rate over the trial period.

There were 1228 women randomised (615 LDA, 613 placebo). Participants had a mean age of 28.7, were mostly white (95%), well educated (86% more than high school education), and employed (75%) with a household income >$100 000 annually (40%). The characteristics of those in the treatment and placebo arms were well balanced.

We describe the study design, recruitment, data collection, and baseline characteristics of participants enrolled in EAGeR, which aimed to determine the effect of LDA on livebirth and other pregnancy outcomes in these women.