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BACKGROUND: Attention deficit hyperactivity disorder (ADHD) is the most common neurobehavioral disorder in children, yet its etiology is poorly understood. Early thyroid hormone disruption may contribute to the development of ADHD. Disrupted maternal thyroid hormone function has been associated with adverse neurodevelopmental outcomes in children. Among newborns, early-treated congenital hypothyroidism has been consistently associated with later cognitive deficits. METHODS: We systematically reviewed literature on the association between maternal or neonatal thyroid hormones and ADHD diagnosis or symptoms. We searched Embase, Pubmed, Cinahl, PsycInfo, ERIC, Medline, Scopus, and Web of Science for articles published or available ahead of print as of April 2018. RESULTS: We identified 28 eligible articles: 16 studies of maternal thyroid hormones, seven studies of early-treated congenital hypothyroidism, and five studies of neonatal thyroid hormones. The studies provide moderate evidence for an association between maternal thyroid hormone levels and offspring ADHD, some evidence for an association between early-treated congenital hypothyroidism and ADHD, and little evidence for an association between neonatal thyroid hormone levels and later ADHD. CONCLUSIONS: The reviewed articles suggest an association between maternal thyroid function and ADHD, and possibly between early-treated congenital hypothyroidism and ADHD. Study limitations, however, weaken the conclusions in our systematic review, underlining the need for more research. Importantly, there was much variation in the measurement of thyroid hormone function and of ADHD symptoms. Recommendations for future research include using population-based designs, attending to measurement issues for thyroid hormones and ADHD, considering biologically relevant covariates (e.g., iodine intake), and assessing nonlinear dose responses., Funding Agency:NIEHS, Grant Number: R01ES021777Intramural Research Program of the NIH, National Institute of Environmental Health Sciences

BACKGROUND: Maternal thyroid function is a critical mediator of fetal brain development. Pregnancy-related physiologic changes and handling conditions of blood samples may influence thyroid hormone biomarkers. We investigated the reliability of thyroid hormone biomarkers in plasma of pregnant women under various handling conditions. METHODS: We enrolled 17 pregnant women; collected serum and plasma were immediately frozen. Additional plasma aliquots were subjected to different handling conditions before the analysis of thyroid biomarkers: storage at room temperature for 24 or 48 hours before freezing and an extra freeze-thaw cycle. We estimated free thyroid hormone indices in plasma based on T3 uptake. RESULTS: High correlations between plasma and serum (>0.94) and intraclass correlation coefficients for plasma handling conditions (0.96 to 1.00) indicated excellent reliability for all thyroid hormone biomarkers. CONCLUSION: Delayed freezing and freeze-thaw cycles did not affect reliability of biomarkers of thyroid function in plasma during pregnancy., Funding Agency:Intramural Research Program, Grant Number: R01ES021777National Institutes of Environmental Health Sciences (NIEHS)National Institutes of Health (NIH)Norwegian Institute of Public Health