RESUMEN
OBJECTIVE: Transient neonatal hyperthyrotropinemia (TNH) is defined as a neonatal abnormality of thyroid function, which reverts to normal at re-examination after 2 weeks of life. The thyroid function of these infants has not been sufficiently studied in terms of the risk of developing persistent hyperthyrotropinemia (PH) in later childhood and its impact on growth and development. DESIGN: A prospective cohort study included all babies born in our hospital between 2001 and 2006 and screened for hypothyroidism, whose thyroid function was re-examined 6 years later. Exclusion criteria included the following conditions: preterm birth, birth weight <2500âg, Down's syndrome, descendants of mothers with immune thyroid disease, congenital malformations, cardiac, renal, hepatic, and metabolic diseases, and steroid or dopamine medication. The variables included are TSH and thyroxine at neonatal screening and 6 years later. Main outcomes are the risk of developing PH in childhood, linear growth, and development using Parents' Evaluation of Developmental Status (PEDS). RESULTS: Out of 5040 normal-term newborns, 301 (6.0%, 95% CI 5.3-6.6%) have TSH ≥10âmU/l (TNH). Six years later, we re-examined 65 randomly selected children with TNH and 185 controls. In the TNH cohort, we found six out of 65 children (9.2%, 95% CI 1.4-17.0%) with PH (TSH ≥6.4âmU/l), and three out of 185 (1.6%, 95% CI 0.3-4.7%) among controls, relative risk 5.7 (95% CI 1.5-22.1), P=0.0114. TSH and developmental delay were found to be significantly higher in the TNH cohort (4.7±1.3âmU/l vs 2.1±0.5âmU/l, P<0.0001 and 15/65 (23%, 95% CI 12-34.1) vs 21/185 (11.3%, 95% CI 6.5-16.2) P=0.0348). CONCLUSIONS: Newborns with TNH have a higher risk of developing PH in childhood, with repercussion on developmental status.