Evaluation of the Thyroid Hormone Status among Normal New Born Preterm Infants

Introduction: Thyroid dysfunction poses a greater risk in preterm newborns (PN) compared to term newborns (TN), often eluding detection in neonatal screening due to delayed thyrotropin (TSH) elevation in these cases. Objective: To assess thyroid function during the second week of life in PN born before 32 weeks gestation and identify factors associated with its alteration. Methods: A retrospective study examined thyroid function in < 32 weeks gestation neonates, analyzing thyroxine (T4L) and TSH levels in relation to perinatal and neonatal outcomes. The study included 358 patients with a mean gestational age of 29.3 weeks and a mean birth weight of 1127 grams. Results: Linear correlations were observed between T4L and birth weight (BW) (R=0.356; p<0.001) and gestational age (GA) (R=0.442; p<0.001). TSH values were associated with small for gestational age (SGA) (5.3 mU/L [1.5-37] for SGA vs. 2.89 mU/L [0.2-19.5] for non-SGA; p<0.001), inotropic support (3.98 mU/L [0.6-22.9] for Yes vs. 3.16 mU/L [0.2-37] for No; p=0.019), and BW (R=-0.249; p<0.001). Levothyroxine treatment was administered to 2.5% of patients, with six being SGA. Conclusions: Analyzing thyroid function in the second week aids in identifying asymptomatic newborns at risk of thyroid dysfunction, particularly in the case of SGA newborns who exhibit a higher susceptibility to thyroid function alterations.