Thyroid function characteristics and early growth and neurodevelopmental outcomes in NICU preterm infants: A retrospective cohort study

To investigate thyroid function characteristics in preterm infants during early life, identify risk factors for thyroid dysfunction, and analyze associations with physical growth and neurodevelopmental outcomes.

A retrospective cohort study was conducted using clinical data from preterm infants admitted to the Neonatal Intensive Care Unit (NICU) between January 1, 2019, and December 31, 2024. Thyroid function parameters within the first month were analyzed. Logistic regression was performed to identify risk factors for thyroid dysfunction. Physical growth and neurodevelopmental outcomes within 12 months were compared between infants with and without thyroid dysfunction using generalized estimating equations (GEE).

The overall incidence of thyroid dysfunction was 59.7% (288/482). The incidence increased with decreasing GA, reaching 95% in those <30 weeks. GA was an independent risk factor, with each one-week increase associated with a 30.2% reduction in risk (OR = 0.698, 95% CI 0.568-0.859). Iodine exposure (OR = 2.572, 95% CI 1.046-6.326) was another independent risk factor. No significant group × time interactions were observed for physical growth (all P > 0.05). For neurodevelopment, significant group × time interactions emerged at 6 months (OR = 2.89, P = 0.020) and 12 months (OR = 4.05, P = 0.003), with the euthyroid group showing decreasing risk and the thyroid dysfunction group showing increasing risk; hyperthyrotropinemia, CH, and low T3 syndrome drove this association. Among infants with thyroid dysfunction, no significant differences were observed between LT4-treated and untreated infants in weight, head circumference, or neurodevelopmental outcomes, except for a modest treatment × time interaction for length at 12 months (β = 0.627, P = 0.034). However, these findings are limited by the single-center, retrospective design.

Thyroid dysfunction was common in NICU preterm infants, driven primarily by small GA and iodine exposure. It is associated with divergent neurodevelopmental trajectories over time, particularly in hyperthyrotropinemia, CH, and low T3 syndrome, but not with physical growth. LT4 treatment did not demonstrate clear benefits.