Aim: For several decades, transient hypothyroxinemia of prematurity is topic of debate. The pathophysiology is incompletely understood and consensus on the therapeutic approach is lacking. This study aimed to obtain more insight in the pathogenesis by studying trends in thyroid hormone levels during the first week of life.
Methods: This single-center prospective observational study studied plasma levels of total and free T4, total T3, TSH and TBG in cord blood and at the end of the first week of life in 120 preterm infants (gestational age < 37 weeks). The change over time was calculated (delta, Δ). The impact of perinatal and subsequently postnatal variables on Δwas studied by hierarchical multiple regression. The impact of Δ on the neurodevelopmental outcome at the corrected age of 9 and 24 months, measured by the Bayley Scale of Infants Development II, was assessed by logistic regression.
Main results: Δ(f)T4 levels were negatively affected by gestational age and use of dopamine, whereas only gestational age was associated with low ΔT3 levels. Negative Δ(f)T4 levels were present in 75% of the extremely-low-for gestational-age infants, whereas 23·5% had a negative Δ T3 level. There was an increased risk for an abnormal mental developmental score (<85) with decreasing ΔT3 at 9 months, corrected age, but not at 24 months.
Conclusions: A negative evolution in circulating thyroid hormone levels is principally an immaturity phenomenon, whereas dopamine can further suppress the hypothalamic-pituitary-thyroid axis. There is at least a temporary negative effect of this evolution on the infants neurodevelopment.
21 Oct 2019
Belgian Endocrine Society