The earlier in gestation the infant is born, the lower neonatal FT4 concentrations will be. Although the first studies showed a relationship between thyroxine levels and neurodevelopmental outcome, recent studies are less conclusive.
Objective To attempt to show a relationship between neonatal FT4 levels and neurodevelopmental outcome at age 5 years in children <31 weeks’ gestation.
Methods Retrospective study; serum FT4 levels measured by radioimmunoassay (FT4 at day 3, mean FT4 between days 4 and 15, 16 and 30 and 4 and 30) in preterm neonates <31 weeks; walking age obtained by calling the general practitioner; neurological status (Touwen test) and cognitive functions (KABC test) assessed at age of 5 years.
Results 176 premature infants born between March 1998 and December 2001 were enrolled. 121 were tested at 5 years of age. The group of non-examined children and the group of examined children were similar in regard to major prognostic factors. In univariate analyse, walking age was correlated to mean FT4 values between day 4 and day 15 (p = 0.04) but not to the other FT4 values. Touwen and KABC scores were not correlated to FT4 values at any time. Multivariate analysis taking in account the most important neurological outcome factors showed no correlation between walking age and FT4 values at either period.
Conclusion Our results suggest that there may not be any benefit in supplementing hypothyroxinemic preterms with T4 hormone.