Research published in the New England Journal of Medicine (1999;341:549–555; 601–602) reported that maternal hypothyroidism during pregnancy may be associated with adverse effects on a child’s cognitive development. Women with untreated thyroid deficiency during pregnancy were found to be four times more likely to have children with lower IQ scores compared with women whose thyroid function was normal.
In this study, 19% of children born to mothers with undiagnosed hypothyroidism during pregnancy had IQ scores of 85 or below. IQ scores in this range are associated with a higher likelihood of learning difficulties in school. Among children aged 7 to 9 years, those whose mothers had untreated hypothyroidism scored an average of seven points lower on IQ testing than children whose mothers had normal thyroid function.
The authors also noted that during the first 12 weeks of pregnancy, the developing fetus relies entirely on the mother for thyroid hormone supply. Adequate maternal thyroid hormone levels during early pregnancy therefore appear to play an important role in normal brain development.
