Abstract
BackgroundBabies born before 28 weeks’ gestation have lower plasma thyroid hormone concentrations than more mature infants. This may contribute to their risk of poor developmental outcome. Previous studies have suggested that thyroxine supplementation for extremely preterm neonates may be beneficial. The aim of this study was to investigate the effect of administration of supplemental thyroxine to very premature babies on brain size and somatic growth at 36 weeks’ corrected gestational age (CGA).MethodsIn this explanatory multicentre double blind randomised placebo controlled trial, 153 infants born below 28 weeks’ gestation were randomised to levothyroxine (LT4) supplementation or placebo until 32 weeks’ CGA. The primary outcome was brain size assessed by the width of the subarachnoid space measured by cranial ultrasound at 36 weeks’ CGA. Lower leg length was measured by knemometry.ResultsBabies in the LT4-supplemented and placebo groups had similar baseline characteristics. There were no significant differences between infants given LT4 (n=78) or placebo (n=75) for width of the subarachnoid space, head circumference at 36 weeks’ CGA, body weight at 36 weeks’ CGA or mortality. Infants who received LT4 had significantly shorter leg lengths at 36 weeks’ CGA although adjusted analysis for baseline length did not find a statistical difference. There was a significant correlation between low FT4 and wider subarachnoid space. No unexpected serious adverse events were noted and incidence of adverse events did not differ between the two groups.ConclusionThis is the only randomised controlled trial of thyroxine supplementation targeting extremely premature infants. Supplementing all babies below 28 weeks’ gestation with LT4 had no apparent effect on brain size. These results do not support routine supplementation with LT4 for all babies born below 28 weeks’ gestation.Trial registrationCurrent Controlled Trials ISRCTN89493983EUDRACT number: 2005-003-09939
Highlights
Babies born before 28 weeks’ gestation have lower plasma thyroid hormone concentrations than more mature infants
LT4 supplementation does not invariably improve neurodevelopmental outcome [6,10,11,12,13,14]. It is unclear whether the condition known as transient hypothyroxinaemia of prematurity (THOP) [15], defined by low FT4 concentrations and normal concentrations of thyroid stimulating hormone (TSH), contributes to the causation of neurodisability
The following were excluded: infants born to mothers with known thyroid disease, on antithyroid medications or amiodarone; infants with major congenital or chromosomal abnormalities known to affect thyroid function or brain development; infants whose mothers died within 5 days of giving birth
Summary
Babies born before 28 weeks’ gestation have lower plasma thyroid hormone concentrations than more mature infants. This may contribute to their risk of poor developmental outcome. The aim of this study was to investigate the effect of administration of supplemental thyroxine to very premature babies on brain size and somatic growth at 36 weeks’ corrected gestational age (CGA). LT4 supplementation does not invariably improve neurodevelopmental outcome [6,10,11,12,13,14] It is unclear whether the condition known as transient hypothyroxinaemia of prematurity (THOP) [15], defined by low FT4 concentrations and normal concentrations of thyroid stimulating hormone (TSH), contributes to the causation of neurodisability. There is clinical uncertainty about whether apparently low plasma FT4 concentrations should be treated or whether they are a marker of illness severity or a normal concomitant of prematurity
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