Purpose: We sought to examine associations among measures of caffeine exposure, including maternal urine, umbilical cord blood, and maternal self report.
Methods: Pregnant women were recruited from 56 obstetric practices and 15 clinics associated with six hospitals in Connecticut and Massachusetts between September 1996 and January 2000; 3633 women were enrolled. Maternal urine throughout pregnancy and umbilical cord blood samples were analyzed for caffeine, paraxanthine, theophylline, and theobromine. Maternal caffeine intake was assessed throughout pregnancy.
Results: Urinary and cord blood biomarkers were correlated with reported intake throughout pregnancy (range r = 0.35-0.66; p < 0.0001). Infants of smokers had greater cord blood concentrations of paraxanthine, reflecting faster caffeine metabolism in smokers, and cord blood paraxanthine levels were more strongly correlated with intake in smokers.
Conclusion: Maternal self reported intake may still be the optimal and most valid measure of antenatal caffeine exposure, since biomarkers do not reflect exposure over pregnancy.