The Effect of Preconception-Initiated Low-Dose Aspirin on Human Chorionic Gonadotropin-Detected Pregnancy, Pregnancy Loss, and Live Birth : Per Protocol Analysis of a Randomized Trial

Ann Intern Med. 2021 May;174(5):595-601. doi: 10.7326/M20-0469. Epub 2021 Jan 26.


Background: A previous large randomized trial indicated that preconception-initiated low-dose aspirin (LDA) therapy did not have a positive effect on pregnancy outcomes. However, this trial was subject to nonadherence, which was not taken into account by the intention-to-treat approach.

Objective: To estimate per protocol effects of preconception-initiated LDA on pregnancy loss and live birth.

Design: The EAGeR (Effects of Aspirin on Gestation and Reproduction) trial was used to construct a prospective cohort for a post hoc analysis. ( NCT00467363).

Setting: 4 university medical centers in the United States.

Participants: 1227 women between the ages of 18 and 40 years who had 1 or 2 previous pregnancy losses and were attempting pregnancy.

Measurements: Adherence to LDA or placebo, assessed by measuring pill bottle weights at regular intervals during follow-up. Primary outcomes were human chorionic gonadotropin (hCG)-detected pregnancies, pregnancy losses, and live births, determined by pregnancy tests and medical records.

Results: Relative to placebo, adhering to LDA for 5 of 7 days per week led to 8 more hCG-detected pregnancies (95% CI, 4.64 to 10.96 pregnancies), 15 more live births (CI, 7.65 to 21.15 births), and 6 fewer pregnancy losses (CI, -12.00 to -0.20 losses) for every 100 women in the trial. In addition, compared with placebo, postconception initiation of LDA therapy led to a reduction in the estimated effects. Furthermore, effects were obtained in a minimum of 4 of 7 days per week.

Limitation: The EAGeR trial data for this study were analyzed as observational data, thus are subject to the limitations of prospective observational studies.

Conclusion: Per protocol results suggest that preconception use of LDA at least 4 days per week may improve reproductive outcomes for women who have had 1 or 2 pregnancy losses. Increasing adherence to daily LDA seems to be key to improving effectiveness.

Primary funding source: National Institutes of Health.

Publication types

  • Multicenter Study
  • Randomized Controlled Trial
  • Research Support, N.I.H., Extramural

MeSH terms

  • Abortion, Spontaneous
  • Adult
  • Anti-Inflammatory Agents, Non-Steroidal / administration & dosage*
  • Aspirin / administration & dosage*
  • Chorionic Gonadotropin / blood*
  • Female
  • Humans
  • Live Birth
  • Medication Adherence
  • Preconception Care / methods*
  • Pregnancy
  • Pregnancy Outcome*
  • United States


  • Anti-Inflammatory Agents, Non-Steroidal
  • Chorionic Gonadotropin
  • Aspirin

Associated data