Association between maternal urinary cotinine concentrations during pregnancy and neonatal blood thyroid-stimulating hormone levels: The Japan environment and Children's study (JECS)

Thyroid hormones are crucial for neurodevelopment and somatic growth, with blood thyroid-stimulating hormone (TSH) levels indicating thyroid function. The effects of maternal smoking on neonatal TSH levels remain inconclusive. In this study, we used data from the Japan Environment and Children's Study to investigate the relationship between maternal urinary cotinine concentrations during pregnancy and neonatal blood TSH levels, stratified by newborn sex. We analyzed data from 52,552 mother–child pairs. Maternal smoking status was categorized as non-smoker, passive smoker, or active smoker based on urinary cotinine concentrations. For visual analysis, cotinine concentrations were divided into deciles. Linear and modified Poisson regression models were used to examine the relationship between maternal smoking and neonatal TSH levels. Increasing maternal urinary cotinine concentrations were associated with higher neonatal blood TSH levels in both sexes, with a more pronounced increase in female newborns. Beyond a specific cotinine threshold, indicative of higher passive smoking exposure, TSH levels declined in both male and female newborns. Passive smoking was significantly associated with increased TSH levels in female newborns compared to those born to non-smoking mothers. No such associations were observed for active smoking status in either male or female newborns. Maternal tobacco smoke exposure during pregnancy was associated with a dose-dependent increase in blood TSH levels in offspring of both sexes. In particular, female neonates whose mothers were exposed to higher levels of passive smoking had the highest risk of elevated TSH levels, suggesting potential adverse effects on neonatal thyroid function.