Yoon SA, et al. - Among extremely low-birth-weight infants (ELBWIs), researchers determined the incidence, etiology, and outcomes of thyroid-stimulating hormone (TSH) elevation. They retrospectively analyzed newborn thyroid screening data of 584 ELBWIs (birth weight, < 1000 g; gestational age, ≥ 23 weeks) to identify initial (≤ 2 postnatal weeks) and delayed (> 2 weeks) TSH elevations. Investigators found that the timing of insult superimposition on hypothalamic–pituitary–thyroid axis maturation is a significant determinant of initial or delayed TSH elevation in ELBWIs. Replacement of levothyroxine in this population did not affect growth or neurodevelopmental outcomes.