Iodine deficiency and neonatal hypothyroidism.

The incidence of neonatal hypothyroidism, as reflected in cord-blood thyroxine and thyrotropin levels, varied from 0.6% to 13.3% in iodine-deficient and normal regions of India (selected districts of Uttar Pradesh and Kerala and the city of Delhi), depending on the degree of environmental iodine deficiency. In populations with a high incidence of neonatal hypothyroidism, an increased prevalence of nerve deafness and a shift to the left in the distribution of IQ scores (towards lower scores) have been demonstrated. These indications of mild brain damage suggest that nutritional iodine deficiency can present in other ways than goitre or cretinism. Determination of the incidence of neonatal hypothyroidism using dried cord-blood spot screening appears to be the most useful and reliable method to assess the risk of brain damage in iodine-deficient areas.