Thyroid function in preterm infants with respiratory distress syndrome.

Thyroid function was evaluated in premature infants 30 to 35 weeks EGA with severe RDS and was compared to that of healthy control subjects of similar EGA. The infants with RDS had significantly lower serum levels of T3, T4, and FT4I during the first 60, 90, and 30 days, respectively, and had elevated T3UR during the first 10 days. The mean (+/- SD) postdelivery TSH peak was lower in the RDS group (32.8 +/- 9.6 muU/ml) than in the control group (60.9 +/- 21.8 muU/ml; P less than 0.005). After TRH injection the increment in serum TSH was inversely related to the basal FT4I in the control infants but not in the infants with RDS.