[Thyroid function in healthy premature infants and in premature infants with the hyaline membrane syndrome ].

The serum concentrations of thyrotropin (TSH), thyroxine (T4), trijodothyronine (T3) and of 3,3',5', trijodothyronine (reverse T3, rT3) were followed up during the first 4 weeks of life in 5 healthy premature infants and in 6 premature infants with hyaline membrane syndrome and artificial ventilation. TSH and T4 concentrations remained unchanged in both groups. T3 levels increased during the observation period and were significantly lower in the sick prematures on days 1 and 3 (p less than 0,02). T3 and the rT3/T3 ratio was increased in healthy and in the sick prematures, the sick prematures showing higher values, and decreased in both groups during the first week of life. We found no significant correlation between TSH and the peripheral thyroid hormone levels as well as no relation between the respiratory compliance-indicating degree of lung maturity-and the T3 or T4 concentrations. Postpartal T3 or T4 serum levels were correlated significantly with the duration of artificial ventilation. Our data indicate that a "low T3 syndrome" was present in all prematures after birth and that respiratory distress syndrome increased conversion of T4 to rT3. From our results we cannot conclude that substitution therapy with thyroid hormones may be useful in premature infants with the hyaline membrane syndrome.