Effect of l-thyroxine supplementation on infants with transient hypothyroxinemia of prematurity at 18 months of corrected age: randomized clinical trial.

Objective: Our objective was to evaluate effects of levothyroxine (l-T4) supplementation against neurodevelopmental outcomes at 18 months of corrected age in very-low-birth-weight (VLBW) infants with hypothyroxinemia but without elevated thyroid-stimulating hormone (TSH) concentration.

Methods: VLBW infants who had plasma TSH concentrations <10 μU/mL and free thyroxine (FT4) concentrations <0.8 ng/dL between 2 and 4 weeks of age were enrolled. They were randomly assigned to either the Treated (n=25) or Untreated group (n=45). The Treated group received l-T4 at a dose of 5 μg/kg/day. We compared growth and neurodevelopmental outcomes at 18 months of corrected age in the two groups.

Results: There were no significant differences in growth, the incidences of developmental delay, cerebral palsy, visual impairment, and hearing impairment in the two groups.

Conclusions: In such infants, l-T4 supplementation at a dose of 5 μg/kg/day did not affect FT4 levels and showed no beneficial effect at 18 months of corrected age.