Research in Medicine

 Background : Recent studies have shown normal thyroid function in infants whose mothers receive methimazole (MMI) during breast-feeding. This study evaluates the long-term effect of MMI on thyroid function and intellectual development of such children.

Methods : 82 children aged 48-86 months were studied. 42 children had been breast-fed while their thyrotoxic lactating mothers received daily doses of MMI 20-30 mg in the first, 10 mg in the second and 5-10 mg for additional 10 months of therapy. Thyroid function of infants remained normal during the one year of MMI therapy of their mothers. 40 other infants served as controls. Serum T4, T3, and TSH concentrations, urinary iodine, thyroid antibodies, intelligent quotient (IQ), verbal and functional (performance) components (Wechsler and Goodenough tests) were measured in all children of case and control groups.

Results : Height, weight, serum T4, T3, TSH and antithyroid antibody titers were not differed between children of case and control groups. The mean IQ was 107±17 vs 106±16 (Goodenough test) and 103±10 vs 103±16 (Wechsler test) for children of thyrotoxic mothers and control children, respectively. There was no difference in verbal and functional IQ and their components between children of thyrotoxic MMI treated mothers and control children.

Conclusion : Thyroid function and physical and intellectual development of breast–fed infants whose thyrotoxic lactating mothers were treated with MMI are normal at age 48 to 86 months.