CORD SERUM THYROID STIMULATING HORMONE (THS) AND THYROGLOBULIN (Tg) LEVELS DO NOT DECLINE WITH INCREASING WEIGHT IN NORMAL NEWBORNS WITH mean ± SD BIRTH WEIGHT OF 3685 ± 623 GRAMS OR GREATER

Abstract

Tg, TSH, free T4 index, and free T3 index were determined in cord serum and related to birth weight and sex in normal newborns, 12 females and 12 males. Free index values are the product of the T3 resin uptake ratio and the appropriate thyroid function indice. Mean ± SD birth weight of female infants (3685 ± 623 grams) was significantly (p <0.025) less than that of male infants (4104 ± 248 grams). In contrast, the mean ± SD free T4 index value of female infants (8.4 ± 0.7 μg/dl) was significantly (p < 0.025) greater than that of male infants (7.3 ± 1.6 μg/dl). Free T3 index values (58.1 ± 4.2 vs 60.5 ± 6.0 ng/dl), TSH values (7.0 ± 3.8 vs 8.4 ± 3.2 μU/ml, and Tg values (39.1 ± 8.1 vs 38.3 ± 12.0 ng/ml) of female and male infants did not differ significantly (p >0.1). Free T4 index values of female (r = 0.804, p < 0.005) and male (r = 0.704, p <0.01) infants correlated positively with free T3 index values. The log of TSH levels did not correlate with birth weight in female infants (r = -0.291, p >0.1). However, male infants showed a positive correlation between the log of TSH levels and birth weight (r = 0.539, p <0.05). Tg levels of female (r = -0.282, p >0.1) or male (r = 0.254, p >0.2) infants did not correlate with birth weight. These data, together with our prior observations, are consistent with a hypothesis that body composition may influence cord serum Tg and TSH levels.