401 Free Thyroxine Levels in the Initial Four Weeks of Life in Extreme Preterm Infants Affect Brain Growth

Abstract

Background: Low blood thyroid hormone concentrations in the first few weeks of life in extremely preterm infants may be linked with poor neurodevelopment. We conducted a multi-centre randomised controlled trial of thyroid hormone supplementation in babies under 28 weeks' gestation. Methods: 78 infants received levothyroxine supplementation and 75 received placebo. There was no difference in overall outcome. A post hoc subgroup analysis was undertaken. FreeT4 (FT4) plasma levels were measured longitudinally during the initial 4 weeks after birth. Two subgroups with average FT4 values in the lowest and highest quartiles were created for each trial arm. Univariate and multivariable analyses comparing the lowest and highest quartiles of FT4 within each trial arm were undertaken. Width of subarachnoid space at 36 weeks corrected for postmenstrual age was used as a measure of brain volume. Results: Among placebo infants, univariate analyses showed that the lowest quartile of FT4 was associated with larger subarachnoid space (smaller brain volume) [95%CI=0.05(0.002,0.09)]. These infants also had higher mortality, lower gestational age and lower birth weight compared with those in the highest quartile. In the thyroxine group, there was no significant difference in subarachnoid space between the lower and higher quartiles. Conclusion: Van Wassanaer (2002) reported that low FT4 levels in the first 4 weeks of birth were associated with worse neurodevelopmental outcome at 5 years in babies born < 30 weeks. Our findings extend their work by suggesting that longitudinal FT4 levels are an independent factor affecting brain growth in babies born < 28 weeks.