Maternal mild thyroid insufficiency and risk of attention deficit hyperactivity disorder

Summary

This study was embedded within the Generation R, a population-based birth cohort in the Netherlands where children were followed up from birth until young adulthood. Of the 4997 eligible mother-child pairs with data on maternal thyroid levels (excluding twins), 3873 pairs of children and caregivers (77.5%) were included in the main analyses. Maternal hypothyroxinemia, characterized by low levels of free thyroxine coexisting with reference thyrotropin levels, and children’s symptoms of attention-deficit hyperactivity disorder (ADHD) were the main outcome measures. Maternal thyroid hormone levels (thyrotropin, free thyroxine, thyroid peroxidase antibodies) were measured at a mean (SD) of 13.6 (1.9) weeks of gestation. Children’s ADHD symptoms were assessed at 8 years of age using the Conners’ Parent Rating Scale-Revised Short Form; higher scores indicate more ADHD symptoms (possible range, 0–36). Maternal hypothyroxinemia (n=127) in early pregnancy was associated with higher scores for ADHD symptoms in children at 8 years of age after adjustments for child and maternal factors (increase in ADHD scores, 7% [95% CI, 0.3%, 15%]). The results remained essentially unchanged when women with elevated levels of thyroid peroxidase antibodies were excluded. The authors concluded that children exposed to maternal hypothyroxinemia in early pregnancy had more ADHD symptoms, independent of confounders. This finding suggests that intrauterine exposure to insufficient thyroid hormone levels influences neurodevelopment in offspring.