[Thyroid function in premature infants of different gestational age during the first month of life (author's transl)].

To assess the function of the thyroid gland in premature infants of different gestational ages during the first month of life we determined simultaneously TSH, T4, T3, and rT3 serum concentrations in 116 preterm infants (gestational ages 31st to 38th week) during each of the first 30 days of life. The serum concentrations of TSH, T3, and rT3 changed significantly during this period. The TSH and rT3 values were highly increased on the first day and decreased thereafter. The T3 values, however, increased significantly during this period. During the first month of life the T4 values remained roughly unchanged independent of the age of the children. There was no significant influence on serum concentrations of thyroid hormones by gestational age. The 65 preterm infants with adaptational disorders showed no difference in their patterns of TSH and thyroid gland activity during the first month of life compared with 51 healthy premature infants. From the 4th to the 6h day of life -- a recommended period for the screening of congenital hypothyroidism -- the differences of TSH values measured were insignificant (16-18 muU/ml). The T4 values on these days remained all above 6.8 microgram/dl.