[Thyroid function and its influencing factors in preterm infants].Zhonghua Er Ke Za Zhi 2026 May 15; 64(6):639-645. [Online ahead of print]ZE
Objective: To investigate the baseline thyroid function status and influencing factors in preterm infants. Methods: A cross-sectional study was conducted, enrolling 2 236 preterm infants with gestational ages of 28-<37 weeks admitted to the Department of Neonatology, Capital Center for Children's Health, Capital Medical University between September 2015 and September 2024, and 912 full-term infants hospitalized for jaundice during the same period. All neonates who enrolled to anaylized underwent first time thyroid function testing between 7-14 days of age. Clinical data, thyroid function levels, maternal pregnancy complications, birth-related and postnatal complications, and therapeutic medications were collected. Preterm infants were stratified by sex and gestational age weeks to describe thyroid function status for comparison with full-term infants. Preterm infants with thyroid function retesting between 37 and <40 weeks were further analyzed and compared thyroid hormone levels of full-term infants with gestational ages of 37-<38 weeks. Inter-group comparisons were performed using the Mann-Whitney U test, with multivariate linear regression analysis to identify influencing factors of thyroid function in preterm infants. Results: Among the 632 neonates who enrolled to anaylized, 354 cases (56.0%) were male and 278 cases (44.0%) were female; 365 cases (57.8%) were preterm infants and 267 cases (42.2%) were full-preterm infants. Female preterm infants exhibited higher serum T4 and T3 levels than males (both P<0.05).TSH was negatively associated with gestational age at birth (β=-0.18, P<0.001). In contrast, T4, FT4, T3, and FT3 were all positively associated with gestational age at birth (β=4.56, 0.39, 0.04, and 0.15, respectively; all P<0.001).In the thyroid function assay, a total of 127 preterm infants with corrected gestational ages ranging from 37 weeks to <40 weeks and 102 full-term infants were included. Comparative results between the two groups showed that the levels of T4, FT4, and T3 were all lower in the preterm infants than in the full-term group (all P<0.01), whereas no statistical difference was observed for TSH and FT3 (both P>0.05). Multivariate linear regression analysis indicated that TSH levels were positively correlated with gestational age and postnatal dopamine use (β=0.34 and 0.10, both P<0.05) and negatively correlated with the Apgar score at the first minute and the presence of patent ductus arteriosus (β=-0.16 and -0.12, both P<0.05). T3 levels were positively correlated with preterm gestational age and female sex (β=0.39 and 0.11, both P<0.05) and positively correlated with preterm gestational age and female sex (β=0.40 and 0.11, both P<0.05), but negatively correlated with the number of pregnancies and the presence of patent ductus arteriosus (β=-0.11 and -0.12, both P<0.05). FT3 levels were positively correlated with gestational age (β=0.34, P<0.05) and negatively correlated with the presence of patent ductus arteriosus (β=-0.11, P<0.05). FT4 levels were positively correlated with gestational age, postnatal neonatal respiratory distress syndrome, and pregnancy-induced hypertension (β=0.37, 0.15, 0.10; all P<0.05), but negatively correlated with the number of pregnancies (β=-0.12, P<0.05). Conclusions: The thyroid function of preterm infants differs from that of full-term infants, with lower birth gestational age being associated with a higher likelihood of transient hypothyroidism. Thyroid hormone levels in preterm infants corrected for gestational age at 37 weeks remain lower than those in full-term infants. In addition to gestational age, thyroid function in preterm infants is also influenced by gender, multiple pregnancies, Apgar score, patent ductus arteriosus, and use of dopamine medications.
