Thyroid hormones (TH) are essential for normal brain development and growth during prenatal and also the early postnatal critical period. The saturation level of receptors of brain cells by TSH is the most valuable indicator, which allows a prediction of possible impairment of mental development for this reason. At the population level, especially in connection with endemic iodine deficiency (ID), it is possible to follow up neonatal TSH in mass screening for congenital hypothyroidism (SCH). Neonatal TSH is the most important factor for monitoring the iodine supply in this age group. In the Czech Republic (CR) the first assessment of iodine supply in the neonate population was performed in an epidemiological study in 3 regions (1993 - 1995). Iodurias, thyroid volumes and TH in 5-day-old newborns and their mothers were estimated (9). The results confirmed mild to moderate ID. In the control study, after 3 years of preventive measures, normalization of the iodine supply in newborns in the followed up regions was found (10). Since 1996 the iodine supply in the Czech newborn population is monitored byTSHvalues obtained fromSCH. Although IDin the 6 - 65 year-old Czech population has been already eliminated, in the highest risk population group a mild ID still persists. TSH (5 - 20 mIU/l), higher than in 3%of newborns is annually recorded with longlasting regional differences. It is necessary to normalize the iodine supply also in this population group as soon as possible with the help and permanent care of health specialists, who are involved in following up pregnant and lactating mothers.

        Key words: maternal hypothyroxinaemia, disturbances of mental development of children, screening of congenital hypothyroidism, neonatal TSH monitoring for iodine supply