Relationships between serum and meconium biomarkers of prenatal tobacco smoke exposure and their association with infant and early childhood growth

Prenatal active and secondhand tobacco smoke exposures remain a prevalent and preventable risk factor for adverse infant and childhood health outcomes. I used a prospective birth cohort of 389 mothers and their infants who were followed from early pregnancy to three years of age to address two specific aims. First, I validated the utility of meconium as a biological matrix to quantify prenatal tobacco smoke exposure. Second, I examined the association between prenatal tobacco smoke exposure and early childhood body mass index (BMI). I validated the utility of meconium tobacco smoke metabolites as biomarkers of prenatal tobacco smoke exposure against self-report and serum cotinine biomarkers of tobacco smoke exposure. I also estimated and compared associations between meconium and serum metabolite concentrations and infant birth weight. Nicotine, cotinine, and trans-3'-hydroxycotinine were detected in the majority of meconium samples (57-80%). Meconium tobacco smoke metabolite concentrations were positively associated with self-report and serum cotinine biomarkers of tobacco smoke exposure. The association between meconium metabolite concentrations and infant birth weight was similar to serum cotinine associations. Meconium is a promising biological matrix to quantify prenatal environmental toxicant exposure; however, meconium tobacco smoke metabolite concentrations did not provide additional information that could be obtained from a single serum cotinine measurement. In the second aim, prenatal tobacco smoke exposures were quantified using maternal self-report and serum cotinine biomarkers. BMI was calculated from weight and height measurements taken at birth, 4 weeks, and 1, 2, and 3 years of age. During pregnancy, 51% of women had cotinine levels consistent with SHS exposure and 10% had cotinine concentrations indicative of active smoking. After adjustment for confounders, both self-report and serum biomarkers of active tobacco smoke exposures were associated with elevated BMI at 2 and 3 years of age. Estimates of association between self-reported SHS exposures and BMI were attenuated towards the null relative to serum cotinine concentration associations. These results suggest that prenatal tobacco smoke exposures may play a role in the development of overweight in early childhood and that self-reported prenatal SHS exposures are non-differentially misclassified, resulting in biased estimates of association with childhood BMI