Normal Serum TSH Concentrations in Korean Newborn Infants and Children

ABSTRACT

To obtain normal serum TSH concentrations in newborn infants and children and to observe the effect of body cooling on serum TSH concentrations during the early postnatal period, the author studied ten newborn infants and one hundred and twenty-two normal and healthy subjects from 3 days to 16 years of age. Immediately after delivery, a group of five newborn infants were placed in a warmed incubator(35-37degrees C) and another group of five newborn infants were placed in a crib at room temperature (22-30degrees C) during the first 48 hours of life. Total two hundred twenty-one blood samples including ten maternal blood, ten cord blood, and umbilical arterial blood drawn through an indwelling catheter at 10, 30, and 60 minutes. 1,2,3 and 4 hours, and femoral venous blood sampled at 24 and 48 hours of life from ten newborn infants were measured by applying radioimmunoassay technique. The results are as follows 1. Mean TSH concentration was significantly higher in cord blood (10.5 microU/ml) compared to maternal blood(6.6microU/ml). This finding suggests a fetal-maternal highly significant TSH gradient at term. 2. In the early postnatal period, serum TSH concentrations increased rapidly to peak level (mean of 74.0microU/ml) at 30 minutes of life and then fell very gradually to mean concentration of 10.3microU/ml at 48 hours of life-the level close to the cord blood concentration of 10.5microU/ml. 3. Mean serum TSH concentrations of various age groups were 10.6microU/ml in neonates of age 3-7 days, 8.1microU/ml in infants of 1-12months, 5.7microU/ml in preschool children of age 1-5 years, 5.8microU/ml in school children of age 6-11 years, and 4.5microU/ml in adolescents of age 12-16 years. 4. The infants group placed at room temperature reached higher peak serum TSH concentrations sooner than the infants group placed in incubators. This difference suggests that extrauterine cooling is capable of increasing TSH secretion in the normal neonates. The elevation in serum TSH concentrations observed in incubated infants indicates that neonatal hyperthyrotropinemia could be caused by stimuli other than exposure to cold.