Thyroid Disorders in Premature and Sick Newborns

ABSTRACT

Thyroid hormone is important in brain development. Thus, thyroid hormone deficiency during the critical period of brain development results in severe cognitive and motor dysfunctions. Along with the development of intensive care for premature infants, the survival rates of premature babies and the long-term complications associated with neurodevelopment and motor function have increased. Premature infants differ from full-term infants in terms of the change in thyroid hormone level after birth because of the immaturity of their hypothalamus-pituitary-thyroid axis. Therefore, the diagnostic and therapeutic criteria for hypothyroidism in premature infants still remain unclear. In addition, as the thyroid function of premature infants can be affected by various diseases or drugs, periodic thyroid function tests are required. Although transient hypothyroxinemia is known to spontaneously recover in most infants, some studies have shown further complications associated with neurodevelopmental disorders. Accordingly, although thyroid hormone therapy in preterm infants has been introduced, its efficacy is yet controversial. In order to understand the thyroid abnormalities observed in premature infants or patients in neonatal intensive care units, this article intends to present a comprehensive review of the physiology of the thyroid gland, transient hypothyroxinemia/delayed thyroidstimulating hormone elevation, and euthyroid sick syndrome that affects thyroid function.