Background: Maternal hypothyroidism and/or hypothyroxinemia have been associated with child's poor neuropsychological development, but the results have been inconsistent.
Methods: The Northern Finland Birth Cohort 1986 included all expected births within a year (9362 women, 9479 children) from the two northernmost provinces of Finland. Maternal serum samples (n = 5791) were obtained in early pregnancy (M ± SD = 10.7 ± 2.8 weeks' gestation), and serum samples from their children were obtained at 16 years of age (n = 5829). All samples were analyzed for thyrotropin, free thyroxine (fT4), and thyroid peroxidase antibodies. The children's school performance was evaluated by their main teachers at eight years of age, as well as by the adolescents themselves at 16 years of age. Data on possible severe intellectual deficiency and mild cognitive limitation were collected from healthcare records and registries for all children. Logistic regression estimated the odds of poor school performance or severe intellectual deficiency/mild cognitive limitation associated with exposure to maternal thyroid dysfunction. The odds of poor school performance associated with the adolescents' own thyroid function at age 16 were also estimated. Results are presented as odds ratios (OR) with confidence intervals (CI), adjusted for maternal/family covariates and child's sex.
Results: Girls of mothers with subclinical hypothyroidism had more self-evaluated difficulties in mathematics than did girls of euthyroid mothers (OR 1.62 [CI 1.06-2.49]). Boys of hypothyroxinemic mothers repeated a school class more often than did boys of euthyroid mothers (OR 5.46 [CI 1.19-25.06]). Adolescents of hyperthyroid mothers had increased odds of poor self-evaluated performance in mathematics (OR 1.61 [CI 1.01-2.49]). Maternal thyroid dysfunction did not increase the odds of a child having severe intellectual deficiency/mild cognitive limitation. At 16 years of age, girls with hyperthyroidism by laboratory measurements had more difficulties in Finnish language (OR 2.82 [CI 1.42-5.61]) than did euthyroid girls. Boys with hypothyroxinemia by laboratory measurement had higher odds of having difficulties in Finnish and/or mathematics (OR 2.13 [CI 1.26-3.62]) than did euthyroid boys.
Conclusions: Maternal thyroid dysfunction during early pregnancy was associated with poorer scholastic performance of the adolescent. Additionally, adolescents' own thyroid dysfunction was associated with difficulties in school performance assessed by self-evaluation.