Mediation of prenatal cotinine and 8-hydroxy-2'-deoxyguanosine levels on infant birth size in the Japan Environment and Children's Study (JECS).

Prenatal passive and active smoking and oxidative stress are of concern because of their adverse effects on infant birth sizes. This study aimed to examine the mediation of maternal cotinine and 8-hydroxy-2'-deoxyguanosine (8-OHdG) levels during pregnancy on infant birth size by occupation. The study used data from 72,544 participants of the Japan Environment and Children's Study (JECS), an ongoing nationwide prospective birth cohort. We used maternal cotinine in urine as a biomarker for prenatal passive and active smoking and maternal 8-OHdG as a biomarker for prenatal oxidative stress. In all participants, multiple linear regression analysis adjusted for covariates showed birth weight (95 % confidence interval; CI) at cotinine level 5 (active smoker level) decreased by 140 (127, 152) g compared to birth weight at cotinine level 1 (non-smoker level), and birth weight at the fourth quartile of 8-OHdG level decreased by 18 (12, 25) g compared to birth weight at the first quartile of 8-OHdG level. When stratified by maternal occupation, no association was found between the cotinine levels of maternal passive smoking exposure and birth size. The association between cotinine levels and decreased birth size in all the participants was mediated by 8-OHdG. The results showed that there was a maternal cotinine levels during pregnancy on birth size in infants.