Thyroid function and intellectual development of children of mothers taking methimazole during pregnancy

Abstract

There is some debate regarding the safety of methimazole (MMI) therapy during pregnancy. It is not known whether MMI therapy in mothers during pregnancy is safe for their children or if it causes alterations in thyroid function and intellectual development during childhood. Twenty-three children, whose mothers were hyperthyroid during pregnancy and treated with MMI 5-20 mg were studied from age 3-11 yr. Thyroid function and liver function tests, urinary iodine, anti-thyroid antibodies, intelligence quotient (IQ), verbal and functional components of Wechsler test were performed on 23 children of thyrotoxic mothers and 30 controls. In all children T3, T4, RT3U and TSH concentrations were normal. Mean T3, T4 and TSH values were 147 ng/dl, 9.7 microg/dl and 1.2 mU/l, respectively. Height, weight, thyroid function, and thyroid antibodies did not differ from controls. None of the children had T4 below 6 microg/dl or TSH>3.0 mU/l. Liver enzymes and serum albumin were normal in both groups. Mann-Whitney test showed no difference in verbal and performance IQ and their components between children of thyrotoxic mothers and controls. Total IQ of cases and controls was 117 +/- 11 and 113 +/- 14, respectively. No deleterious effect occurred in thyroid function and physical and intellectual development of children whose mothers were treated during pregnancy with doses of MMI up to 20 mg daily.

Management of hyperthyroidism during pregnancy and lactation

“…Effect on pediatric physical and mental growth No differences in thyroid function or physical and psychomotor development has been found between children born to MMI-or PTU-treated hyperthyroid mothers during pregnancy and those born to euthyroid mothers (43,44).…”

The safety and efficacy of antithyroid drugs

“…However, no increase in frequency of congenital anomalies in infants exposed to methimazole in utero have been reported by others [84], and at least one case of chronal atresia has been reported in a newborn exposed to propylthiouracil [85]. Studies have shown that school-aged children who were exposed to thionamides, in particular methimazole, during intrauterine life have normal thyroid function and physical and intellectual development [86][87][88].…”

Treatment of Graves’ Disease During Pregnancy

“…Total IQ for the methimazole-treated group was 11711; IQ for the control group was 11314. The authors concluded that no detrimental effects on the physical or intellectual development occurred in those children exposed to methimazole during pregnancy (Azizi, 2002). The main strength of this study was the single blinded psychologist evaluation of child intellect using the WPPSI exam.…”

“…Azizi et al evaluated the methimazole's effect on intellectual development of children whose mothers received methimazole during pregnancy but not during lactation (Azizi, 2002). The authors identified 23 children, ages 3 to 11 years, of mothers who were treated with methimazole during pregnancy and 30 children, ages 3 to 11 years, of mothers who were not treated with methimazole during pregnancy.…”