Circulating levels of T4, T3 and TSH in newborns during the first 7 days of life.

ABSTRACT

Serum total thyroxine (TT4) and triiodothyroxine (TT3) by radio-immunoassay and thyrotropin (TSH) by immunoradiomebtric assay were measured in the sera of full-term normal newborn infants of both sexes during the first 7 days of life. The results indicated that the mean (+ SE) value of TT4 (11.60 + 0.24 ug/dl) was slightly above our normal adult range while the mean of TT3 (97.48 + 2.84 ng/dl) was within the normal adult range. The levels of serum TSH in the newborns increased markedly at the first day after birth and decreased gradually after 3-7 days of postnatal life with the mean value of 5.02 + 036 nU/l. Thus the normal ranges based on the 95%confidence limits for the results of TT4 (5.00-21.00 ug/dl), TT3 (41.00-195.00 ng/dl) and TSH (0.30-18.00 mU/l) in the neonates were established in order to discriminate euthyroid infant from thyroid disorders of infancy. Serum TT3 and TSH levels of newborns during the first 3 days were found to be significantly higher than those of newborns during 4-7 days (p < 0.005). Moreover, significant sex difference was also obtained in the present study because serum TT4 and TT3 levels of the female infants were statistically higher than those of the male infants, p<0.01 and p<0.05, respectively. In addition, the concentrations of TT4 TT3 and TSH were determined and compared in these newborns following normal labour, caesarean section, gorceps and vaccuum extraction. There was a sharp increase in the mean values of serum TT4 TT3 and utilizing elective caesarean section, while a marked increase in the TSH mean was observed by the methods of forecps extraction and also caesarean section.