Thyroid Dysfunction and the Effect of Iodine-Deficient Parenteral Nutrition in Very Low Birth Weight Infants: A Nationwide Analysis of a Korean Neonatal Network Database

Background: To investigate the impact of nutritional iodine deficiency on thyroid dysfunction (TD) in very low birth weight (VLBW) infants, we analyzed the association between iodine-deficient parenteral nutrition (PN) and TD requiring L-thyroxine (TD-LT4). Methods: Data of VLBW infants were obtained from the Korean Neonatal Network registry. Factors including duration of PN were analyzed according to TD-LT4. Results: TD-LT4 occurred in 490 (8.7%) of 5635 infants, and more frequently occurred in infants requiring PN for ≥4 weeks (10.2%). PN ≥ 4 weeks was one of the risk factors for TD-LT4, with an odds ratio (OR) of 1.346, p = 0.002. However, multivariate analysis showed that TD-LT4 was more of a risk for infants that were small for gestational age (OR 2.987, p < 0.001) and for other neonatal morbidities such as seizures (OR 1.787, p = 0.002) and persistent pulmonary hypertension (OR 1.501, p = 0.039) than PN ≥ 4 weeks (OR 0.791, p = 0.080). Conclusions: Prolonged iodine-deficient PN might affect TD-LT4 in VLBW infants. However, the effect of nutritional iodine deficiency on TD-LT4 risk was less than that of SGA or severe neonatal morbidities in Korean VLBW infants.