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10: Preconception low dose aspirin and preterm birth: findings from the EAGeR (Effects of Aspirin in Gestation and Reproduction) randomized trial

      Objective

      To evaluate the effect of low dose aspirin (LDA) initiated preconceptionally on the risk of preterm birth (PTB, live birth at <37 weeks’ gestation).

      Study Design

      The EAGeR trial was a multi-center, randomized, double-blind, placebo-controlled trial of 1,228 US women conducted in 2006-2012. Women 18 to 40 years old with a history of pregnancy loss trying to conceive were eligible for the study. Participants were stratified based on eligibility criteria: 1) original: women with 1 pregnancy loss at <20 weeks’ gestation during the past 12 months; 2) expanded: women with 1-2 prior losses, regardless of gestational length or recency. Participants were block-randomized by study center and stratum to either daily LDA (81 mg, n=615) or an identical looking placebo (n=613). Participants were followed for 6 menstrual cycles or through gestation if they became pregnant. Pregnancy end date was assessed by post-partum interview and medical record review. Gestational age was determined by an ultrasound conducted in early pregnancy for 98% of pregnancies conceived during the study.

      Results

      Approximately 88% (n=1078) of randomized participants completed the study. In the intent-to-treat analysis, PTB risks were: overall, 4.1% (22/535 LDA) and 5.7% (31/543 placebo) (p=0.22); in the original eligibility stratum, 2.9% (7/242 LDA) and 6.4% (16/250 placebo) (p=0.06); and in the expanded stratum, 5.1% (15/293 LDA) and 5.1% (15/293 placebo) (p=1.0). After restriction to confirmed pregnancies, the PTB risks were 5.9% (22/374 LDA) and 9.0% (31/346 placebo) (p=0.12). Using inverse probability weighting to account for different rates of conception by intervention arm, the PTB risks were 3.8% (LDA) and 5.7% (placebo) (p=0.15).

      Conclusion

      Preconception LDA was not significantly associated with the risk of PTB. However, we observed a trend towards lower PTB in the LDA study arm within the confirmed pregnancies and the original eligibility stratum, which warrants further investigation.