Thyroid function in preterm newborns; is T4 treatment required in infants <27 weeks' gestational age?

Thyroid hormones are essential for brain maturation. Very preterm infants, who are at risk of neurodevelopmental disabilities also have low T4 and FT4 values in the first weeks after birth. This transient hypothyroxinemia may in part be causal to the neurodevelopmental problems. We have carried out a randomised, double-blind, placebo-controlled trial with T4 in 200 infants <30 weeks' gestation. In the study groups as a whole (n = 100 in the T4 group, n = 100 in the Placebo group), no clear effect of T4 administration was found. In this study we examined whether gestational age influenced the effect of T4 administration. The T4- and placebo groups were subdivided into 4 groups according to gestational age. FT4-values during the first weeks after birth were lowest in the youngest gestational age group in the T4 as well as in the placebo group. In this group with infants <27 weeks' gestation mental developmental outcome at 2 years of age was significantly better than in the placebo group of the same gestational age. There was also a trend towards a better psychomotor and neurological outcome. Beyond 27 weeks' gestation, no clear effect of T4 could be found; on the contrary, a possible harmful effect on mental developmental outcome might be the result. In conclusion. T4 treatment possibly improves developmental outcome in infants <27 weeks' gestation, but seems not necessary beyond this gestational age