Thyroid hormone supplementation in preterm infants born before 28 weeks gestational age and neurodevelopmental outcome at age 36 months

Thyroid hormones are required for normal brain maturation, and neonatal plasma thyroid hormone concentrations are low in infants less than 28 weeks gestation. It is not known whether treatment of such infants with thyroid hormone improves neurodevelopmental outcome. At three years corrected age, mental, motor, and neurological development was assessed in infants born at less than 28 weeks gestational age who had participated in a phase 1 trial of differing doses and modes of administration of thyroid hormone. The trial's endpoints were thyroid hormone (thyroxine, T4) and thyotropin plasma concentrations in eight study arms: six treated with T4 [4, 8, and 16 μg/(kg · day)], bolus or continuous], one treated with iodine only, and one treated with placebo. Follow-up at three years was not part of the original study goals. Developmental index scores, rates of cerebral palsy (CP), and rates of adverse outcome (death or moderate to severe delay in development and/or disabling CP) were compared between the eight study groups and between groups combined by dosage level, and between infants with and without T4 supplementation. Of 166 randomized infants, 32 (19%) died in the neonatal period. Of the 134 survivors, follow-up results were available for 89 children (66%). Mental and motor development and rates of cerebral palsy did not differ in any of the comparisons made. In this study, no differences in neurodevelopment were found in relation to thyroid hormone treatment, but power was insufficient to detect any but very large differences