Factors Affecting Neonatal Thyroid Function in Preterm Infants

Abstract

Thyroxine is essential for optimal brain development during gestation and for the first 2 years postnatally. Maintaining adequate thyroid hormone levels is vital, as low levels (even transiently low) are associated with adverse neurodevelopmental outcome. Thyroid hormone levels are gestationally age related, and levels vary appreciably between term infants and those born preterm; so much so, that interpretation of levels in preterm infants is most appropriately done against norms specific to the gestation at birth. Several factors, other than gestation, can alter levels of thyroid hormones, thyroid stimulating hormone/thyrotropin, and thyroid binding globulin; knowledge of these factors is helpful for interpretation and when considering the need for replacement therapy. This review focuses on preterm infants and describes the influences of gestation, critical illness, infection, specific neonatal conditions, prescribed drug usage, iodine deficiency, and iodine excess on levels of neonatal thyroid hormones, thyroid binding globulin, and thyroid stimulating hormone/thyrotropin.