Dynamic variations of thyroid function and risk factors for hypothyroidism and delayed thyroid stimulating hormone elevation in late preterm infants / 中华围产医学杂志

ABSTRACT

Objective:To investigate the dynamic changes of thyroid function and risk factors of hypothyroidism and delayed thyroid stimulating hormone (TSH) elevation in late preterm infants.Methods:This study retrospectively recruited 782 late preterm infants admitted to Nanjing Medical University First Affiliated Hospital and performed thyroid function monitoring from January 2017 and December 2019. Thyroid function test was performed in all cases at 4-7 d after birth and repeated at 2-4 weeks of age for those with normal results or two weeks after the first test for those with abnormal. The test would be continued if the second test was abnormal and stopped until the thyroid function became normal or hypothyroidism was diagnosed, based on which, these infants were divided into hypothyroidism ( n=11) and non-hypothyroidism groups ( n=771), or delayed TSH elevation ( n=71) and normal thyroid function groups ( n=450). The characteristics of thyroid hormone changes and perinatal data were compared between different groups using two independent sample t-test and Chi-square test, and risk factors of hypothyroidism and delayed TSH elevation were analyzed using logistic regression tests. Results:(1) Dynamic changes of thyroid function among these 782 late preterm infants, five infants were found with transient hypothyroxinemia at the first test, and became normal at the second test; 249 (31.8%) exhibited hyperthyrotropinemia, and four of them were diagnosed with hypothyroidism based on the second and the third results; 71(9.1%) with delayed TSH elevation all became normal later; 11(1.4%) were diagnosed with hypothyroidism and treated with thyroxine, among which, seven cases were diagnosed at the first test, three at the second test and one at the third test. (2) Risk factors for hypothyroidism lower birth weight was noted for infants with hypothyroidism compared with those without [(2 140.9±455.1) vs (2 464.1±474.0) g, t=-2.247, P=0.025]. Multivariate logistic regression analysis found that for every one gram reduction in birth weight, the risk of hypothyroidism elevated by 0.002 times ( OR=1.002, 95% CI 1.000-1.004, P=0.045). (3) Risk factors for delayed TSH elevation the birth weight was lower [(2 395.4±420.9) vs (2 523.6±462.3) g, t=-2.200, P=0.028], and the proportion of small for gestational age and twin pregnancy were higher in the delayed TSH elevation group than those in the normal thyroid function group [15.5% (11/71) vs 7.1% (32/450), χ2=5.690, P=0.017; 29.6% (21/71) vs 18.7% (84/450), χ2=4.537, P=0.033]. Multivariate logistic regression analysis found that small for gestational age ( OR=4.366, 95% CI 1.649-11.564, P=0.003) and twin pregnancy ( OR=1.943, 95% CI 1.048-3.600, P=0.035) were independent risk factors for delayed TSH elevation. Conclusions:Late preterm infants have a high incidence of different kinds of thyroid dysfunction. Thyroid function monitoring is necessary for late preterm infants because those with lower birth weight are more susceptible to develop hypothyroidism, and those small for gestational age infants and twins are more susceptible to develop delayed TSH elevation.