Caffeine and miscarriage risk.

BACKGROUND: Coffee and caffeine have been inconsistently found to be associated with increased risk of clinical miscarriage-a potentially important association given the high prevalence of exposure.

METHODS: Women were recruited before or early in pregnancy and interviewed regarding sources of caffeine, including assessment of changes over the perinatal period. We identified 2407 clinically-recognized pregnancies resulting in 258 pregnancy losses. We examined the relationship of coffee and caffeine intake with clinically-recognized pregnancy loss prior to 20 weeks' completed gestation, using a discrete-time continuation ratio logistic survival model.

RESULTS: Coffee and caffeine consumption at all 3 time points were unrelated to total miscarriage risk and the risk of loss after the interview. Reported exposure at the time of the interview was associated with increased risk among those with losses before the interview.

CONCLUSIONS: There is little indication of possible harmful effects of caffeine on miscarriage risk within the range of coffee and caffeine consumption reported, with a suggested reporting bias among women with losses before the interview. The results may reflect exposure misclassification and unmeasured heterogeneity of pregnancy losses.