Associations of Respiratory Distress Syndrome Severity and Other Factors With Transient Hypothyroxinemia of Prematurity

Aim This study examined the associations of respiratory distress syndrome (RDS) severity and other factors on thyroid hormone levels in very low birth weight (VLBW) infants. Methods The demographic characteristics, clinical course, morbidity, and initial thyroid function test results of VLBW infants diagnosed with RDS between July 2016 and September 2018 were obtained retrospectively. RDS severity was determined according to the requirement for multiple surfactants. Patients were divided into groups without and with hypothyroxinemia, and variables of interest were compared between the two groups. Results Our study involved 98 infants meeting the inclusion criteria; the incidence of hypothyroxinemia was 56.1%. Free T4 (fT4) levels were found to be negatively correlated with gestational week (p < 0.001) and birth weight (p < 0.001). The fT4 levels were significantly lower in infants requiring multiple surfactant doses. In infants with hypothyroxinemia, the duration of invasive mechanical ventilation and oxygen treatment was longer and hemodynamically significant patent ductus arteriosus, grade ≥ 3 intraventricular hemorrhage, and moderate to severe bronchopulmonary dysplasia were more common. Multiple pregnancy (odds ratio (OR) = 5.616, 95%; confidence interval (CI): 1.765-17.874) and the duration of invasive mechanical ventilation (OR = 1.05, 95%; CI: 1.005-1.096) were significant risk factors for the development of hypothyroxinemia in logistic regression analysis. Conclusions Transient hypothyroxinemia of prematurity is associated with RDS severity and early morbidities of prematurity. In the presence of multiple pregnancy, patients should be followed up more closely due to the possibility of hypothyroxinemia.