Aspirin use and miscarriage risk.

Background: Recent research has found nonsteroidal antiinflammatory drugs, including aspirin, to increase the risk of miscarriage. The objective of the present study was to evaluate the association between aspirin use and miscarriage.

Methods: We conducted a case-control study using data from the Collaborative Perinatal Project. This prospective cohort study recruited approximately 54,000 pregnant women at 12 sites in the United States from 1959 to 1965. Women who had miscarriages (n = 542) were matched by clinic and time in pregnancy when they came under observation to 2587 women who had live births. Participants were interviewed at each prenatal visit. Data on aspirin use were collected prospectively by in-person interviews and medical record review. Aspirin use among controls was considered only for the duration of pregnancy when the matched cases remained pregnant. The outcome of interest was miscarriage, defined as spontaneous pregnancy loss at less than 140 days from the last menstrual period.

Results: Twenty-nine percent of cases and 34% of controls used aspirin during pregnancy. Aspirin use was not associated with an increased risk of miscarriage. Adjusted odds ratios ranged from 0.64 to 0.92 (95% confidence intervals = 0.48-1.38) for individual lunar months and combinations of lunar months.

Conclusions: Use of aspirin during pregnancy is not associated with an increased risk of miscarriage.