Caffeine Intake During Pregnancy, Late Miscarriage, and Stillbirth

Many obstetric guidelines recommend limitation of caffeine intake immediately before and during pregnancy, despite the lack of consistent evidence showing a clear benefit. Although some observational cohort studies have suggested that maternal caffeine intake may be associated with decreased birth weight and fetal growth restriction, in the only reported intervention trial, no substantial effect of caffeine reduction during the second half of pregnancy was found. Evidence for an association between consumption of caffeine and miscarriage earlier in pregnancy may be stronger, but there are no large well-conducted effectiveness trials. This prospective observational cohort study examined the association of maternal caffeine intake with late miscarriage and intrauterine fetal death (stillbirth), using a detailed caffeine assessment tool. The study population included 2643 pregnant singleton women, aged 18 to 45 years, between 8- and 12-weeks' gestation, who attended 2 UK maternity units between 2003 and 2006. Caffeine intake was assessed at different stages of pregnancy, and the pregnancies were monitored for the occurrence of late miscarriage and stillbirth. The data were adjusted for potential confounders, including alcohol intake and smoking status. Total caffeine intake was quantified from all possible sources in the first trimester and throughout pregnancy. The adjusted data showed a strong association between caffeine intake in the first trimester and subsequent late miscarriage between 12 and 24 weeks or stillbirth after 24 weeks. The geometric mean caffeine intake during the first trimester among women whose pregnancies resulted in late miscarriage or stillbirth was higher (145 mg/d, with a 95% confidence interval [CI] of 85-249) compared with those with live births (103 mg/d; with a 95% CI of 98-108). Compared to women with caffeine consumption of 100 mg/d, the adjusted odds ratio for late miscarriage or stillbirth increased to 2.2 (95% CI, 0.7-7.1) for ingestion between 100 and 199 mg/day, to 1.7 (0.4-7.1) for those taking between 200 and 299 mg/d, and to 5.1 (1.6-16.4) for those ingesting over 300 mg/d (P(trend) = 0.004). These findings from a small study suggest that increases in late miscarriage and stillbirth are associated with greater caffeine intake during pregnancy, and support observational evidence on which current guidelines are based.