Congenital hypothyroidism: physiological and psychological factors in early development.

Children diagnosed as congenitally hypothyroid and treated from a very early age were followed up at 1 and 3 years. At 1 year they seemed to be developing normally, unless they were undertreated or had an additional disorder. There were no significant correlations between biochemical or social factors and psychological outcome at 1 year. At 3 years, however, those children whose T4 and/or T3 had been very low initially had significantly lower IQ scores than both other hypothyroid children and matched controls. Children with only moderately low initial T4 and/or T3, however, were doing just as well as their matched controls. Initial levels of TSH, the number of symptoms at first clinical interview and the age at the start of treatment were not good indicators of ability at 3 years. Undertreatment was rare but did appear to affect ability. Psychological outcome at 3 years was also correlated with social class (for both cases and controls). Multiple regression analyses indicated that both low initial T4 (less than 20 nmol/l) and social class contributed significantly to outcome.