Maternal Thyroid Function in Early Pregnancy and Neuropsychological Performance of the Child at 5 Years of Age

Context: Abnormal maternal thyroid function in pregnancy may impair fetal brain development, but more evidence is needed to refine and corroborate the hypothesis. Objective: To estimate the association between maternal thyroid function in early pregnancy and neuropsychological performance of the child at 5 years of age. Design: Follow-up study. Participants: A cohort of 1153 women and their children sampled from the Danish National Birth Cohort. Maternal thyroid-stimulating hormone (TSH) and free thyroxine (fT4) were measured in stored biobank sera from early pregnancy. Main outcomes measures: Child neuropsychological test results (Wechsler Intelligence Scale/Test of Everyday Attention), test of motor function (Movement Assessment Battery), and results of parent and teacher reports (Behavior Rating Inventory of Executive Function/Strengths and Difficulties Questionnaire). Results: Altogether 145 children (12.6%) were born to mothers with abnormal thyroid function in the early pregnancy. High maternal TSH and low fT4 were associated with lower child verbal intelligence quotient (adjusted mean difference TSH >= 10 mIU/L vs 0.1 to 2.49 mIU/L, -8.9 [ 95% confidence interval (CI), -15 to -2.4]; fT < 10 pmol/l vs 12.0 to 18.99 pmol/l, -13 [ 95% CI, -19 to -7.3]). Abnormal maternal thyroid function was also associated with adverse motor function and teacher-reported problems of executive function and behavior, and these associations were dominated by exposure to maternal hypothyroxinemia. Conclusions: Maternal thyroid hormone abnormalities were associated with adverse neuropsychological function of the child at 5 years of age. For intelligence, marked hypothyroidism was important, whereas for motor function and executive and behavior problems, maternal hypothyroxinemia was predominant.