Intellectual development in children with congenital hypothyroidism in relation to recommended thyroxine treatment

J Pediatr. 1991 Jun;118(6):850-7. doi: 10.1016/s0022-3476(05)82194-8.


The relationship between the treatment serum thyroxine level and intellectual development at 2 and 6 years was investigated in 46 Norwegian children with congenital hypothyroidism identified by neonatal screening. The level of serum thyroxine during the first 2 years was positively correlated with the Mental Development Index at 2 years of age (Bayley Scales of Infant Development) and the Verbal IQ at 6 years of age (Wechsler Preschool and Primary Scale of Intelligence). Children with a mean serum thyroxine level greater than 180 nmol/L (14 micrograms/dl) during the first year had a significantly higher Mental Development Index at 2 years and Verbal IQ at 6 years than children with serum thyroxine values less than 129 nmol/L (10 micrograms/dl). Boys had a lower Mental Development Index at 2 years of age than girls (86.9 vs 105.1; p less than 0.001) and a higher frequency of elevated serum levels of thyroid-stimulating hormone during the first year (p = 0.001). No signs of toxic effects of a high hormone level at the time of IQ assessment were detected. However, high serum levels of thyroxine at ages 2 to 4 years in girls were related to lower Performance IQ at age 6 years. The results demonstrate that the serum level of thyroxine is of importance in relation to intellectual development. Thyroxine levels above the upper reference range during the first 2 years were related to best intellectual development at 2 and 6 years.

Publication types

  • Research Support, Non-U.S. Gov't

MeSH terms

  • Analysis of Variance
  • Child
  • Child Development / drug effects*
  • Child Development / physiology
  • Child, Preschool
  • Cohort Studies
  • Congenital Hypothyroidism*
  • Female
  • Humans
  • Hypothyroidism / drug therapy
  • Intelligence / drug effects*
  • Intelligence / physiology
  • Intelligence Tests
  • Male
  • Sex Characteristics
  • Thyrotropin / blood*
  • Thyroxine / blood*
  • Thyroxine / pharmacology
  • Thyroxine / therapeutic use


  • Thyrotropin
  • Thyroxine