The nature of hypothyroxinemia in sick very low-birth-weight (VLBW) infants was evaluated by assessment of the hypothalamic-pituitary axis and by the clinical response to thyroxine (T4) therapy. Twenty-three very low-birth-weight infants of gestational age 26 to 28 weeks, whose serum T4 concentrations were 4 µg/dL on two occasions, and thyrotropin < 20 µU/mL, were included in a double-blind study. Following a thyrotropin-releasing hormone stimulation test, babies were given either T4 or placebo. Nine babies were thyrotropin-releasing hormone tested prior to therapy; four babies, two from each group, were tested 1 to 2 weeks after therapy. In 11 untreated babies, mean base line serum thyrotropin of 7.0 ± 1.4 rose to 23.7 ± 4.1 µU/mL in 30 minutes. This response was not significantly greater than the observed response in full-term babies, 23.7 ± 4.1 v 16.6 ± 0.97 µU/mL, respectively, P > .05. In two babies treated with T4 the thyrotropin response to thyrotropin-releasing hormone was completely suppressed. Serial serum T4 determinations showed normalization in both groups after a similar time interval. There was no beneficial effect of T4 therapy on growth of head circumference, length, or weight. Developmental data revealed no significant differences in the mental, motor, or gross neurologic outcome in the treated and nontreated infants after 1 year of follow-up. These observations imply that hypothyroxinemia in sick preterm infants is not a direct consequence of hypothyroidism. Despite the lack of demonstrable short-term beneficial effects of T4 therapy, follow-up studies are necessary to resolve the question of long-term benefits.
- idiopathic respiratory distress syndrome
- thyrotropin-releasing hormone.
- Received December 20, 1982.
- Accepted April 26, 1983.
- Copyright © 1984 by the American Academy of Pediatrics