Thyroid Dysfunction in Premature Infants

ABSTRACT

PURPOSE: Severe neonatal hypothyroxinemia is associated with leukomalacia, intraventicular hemorrhage and long-term neurodevelopmental disability. We designed this study to evaluate the incidence of thyroid dysfunctions and the effects of low T4 level on neonatal morbidity to establish the basis for the thyroid hormone supplementation. METHODS: Thyroid function tests, measured by radioimmunoassay and filter paper screening, were obtained from the preterm infants with birth weights less than 2000 g. The first measurement was done during 2nd week of life followed by the measurement at 2 weeks later and repeated until normalized. RESULTS: 17/32 (53.1%) infants had thyroid dysfunction: Four infants had hypothyroidism, twelve infants had hypothyroxinemia and one infant had hyperthyrotropinemia. The frequency of thyroid dysfunction showed inverse relationship to the birth weight. All infants with birth weights less than 1, 000 g, 11 infants (70.6%) with birth weights between 1, 000 and 1, 499 g and two infants (18.2%) with birth weights more than 1500 g had thyroid dysfunction. Nine infants with thyroid dysfunction were not detected by filter paper screening test. Infants with hypothyroxinemia had more RDS, longer mechanical ventilation days and hospital stay compared to the infants with normal T4 level. CONCLUSION: Thyroid dysfunction is frequently observed in premature infants and it can be associated with increased neonatal morbidity. Serial follow up of thyroid function test is recommened among premature infants.