Relationship between free T4 levels and postnatal steroid therapy in preterm infants

Abstract

Transient hypothyroxinemia is the most common thyroid dysfunction in preterm infants. Hypothalamic-pituitary-thyroid immaturity and non-thyroidal illness contribute to its etiology. The aim of the present study was therefore to determine the relationship between thyroid hormone status and early postnatal steroid therapy in preterm infants. A prospective study of premature infants born at <28 weeks of gestation between July 2001 and June 2007 was conducted. Selective postnatal steroid (dexamethasone) therapy was used in lung disease treatment if the infants needed high mean airway pressure-assisted ventilation and supplemental oxygen at 2 weeks of age. Free T4 (FT4) and thyroid-stimulating hormone (TSH) levels were assessed at 2 weeks after birth. Blood samples in eight infants were available after starting steroid therapy. Infants receiving steroids (steroid (+); n= 8) were compared to those not receiving steroids (steroid (-); n= 73). The demographic data were not significantly different between the two groups. The neonatal illnesses and drug use were also not significantly different between the groups. The steroid (+) group had significantly lower FT4 and TSH levels at 2 weeks after birth than the steroid (-) group. The increase in FT4 levels after steroid withdrawal was greater than that during the same period in the steroid (-) patients. Even if it cannot be excluded that reduced FT4 and TSH concentrations are caused by non-thyroidal illness, the present study suggests that postnatal steroid treatment reduces the FT4 and TSH levels in premature infants born at <28 weeks of gestation.