is thyroxine treatment necessary?
Fisher DA Quest Diagnostics, Nichols Institute, San Juan Capistrano, California 92690, USA. Fisherd@questdiagnostics.com The increased survival of very low birth weight (VLBW) premature infants has been associated with an increased prevalence of transient disorders of thyroid function during the early weeks of life. All VLBW infants have relatively low, and gestation age-dependent, thyroxine-binding globulin (TBG) concentrations associated with variably low total thyroxine (T4) concentrations. These infants also have a high prevalence (30%-60%) of nonthyroidal illnesses that impact thyroid function, including total and free iodothyronine concentrations. Finally, thyroid gland hormone biosynthesis and the hypothalamic-pituitary axis are relatively immature and thyroid glandular iodine stores are low. As a result, VLBW infants manifest a high prevalence of transient primary hypothyroidism (0.41%) and transient hypothalamic-pituitary (thyrotropin [TSH] deficiency) hypothyroidism (5%-10%?)