Trimester and sex-specific associations of maternal thyroid profile with neonatal thyroid-stimulating hormone.

Background: Maternal thyroid hormones have been shown to affect neonatal thyroid function. However, it remains unclear whether these associations persist across trimesters, and also little is known regarding the potential effects of mixtures. Objective: This study aimed to examine the effects of maternal thyroid hormones as individual and as mixtures across three trimesters on neonatal thyroid stimulating hormone (TSH). Methods: We included 2,139 pregnant women. Maternal thyroid hormones (TSH, free triiodothyronine (FT3), and free thyroxine (FT4)) across three trimesters and neonatal TSH level were measured. Multivariable linear regression models and Bayesian kernel machine regression (BKMR) models were used to examine the associations between maternal thyroid hormones (individual and mixtures) across three trimesters and neonatal TSH. Results: Maternal TSH demonstrated the positive associations with neonatal TSH across three trimesters (first trimester: β = 0.112; 95% CI: 0.008, 0.215; second trimester: β = 0.122; 95% CI: 0.032, 0.212; third trimester: β = 0.115; 95% CI: 0.031, 0.200). Neonatal TSH was also positively associated with maternal FT4 in the third trimester (β = 1.313; 95% CI: 0.367, 2.239). Moreover, we found sex-specific associations, and the positive associations of maternal TSH and FT4 with neonatal TSH in the third trimester were observed only among female infants, while the positive association of maternal TSH with neonatal TSH in the second trimester was observed only among male infants. The overall positive associations of the mixtures were observed, and maternal TSH was identified as the major contributor. Conclusion: Maternal thyroid hormones affect neonatal thyroid function across all three trimesters by fetal sex.