Abstract
Background: Preterm infants may present mildly elevated levels of TSH (MELTSH) that is levels higher than the '“normal” ones (5 mU/L) but lower than the cut off level of congenital hypothyroidism (20 mU/L). It has been suggested that these MELTSH may indicate hypothyroidism requiring treatment even with normal free thyroxine levels. The aim of this study was to determine the rates of MELTSH in preterm neonates at the first six weeks of life and whether this condition is a transient one.Methods: The study population consisted of 146 healthy preterm neonates (28–36 weeks of gestation) with MELTSH and FT4 serum levels >6 pg/ml. TSH levels were measured by chemiluminescence immunoassay and FT4 levels by RIA method at 2, 4 and 6 weeks of life. Among them 45 (31%) were small for gestational age (SGA) with a birthweight <10th percentile. The rates of MELTSH between SGA and appropriate for gestational age (AGA) neonates were compared by chi-square test. A multivariate logistic regression analysis was applied to evaluate the influence of possible risk factors (gestational age, birth weight, fetal distress, maternal chorioamnionitis, etc) on the incidence of MELTSH.Results: MELTSH was found in 79/146 neonates (54%) in 44/146 (30%) and in 24/146 (16.5%) at the 2nd, 4th and 6th week respectively. The incidence of neonates with MELTSH did not differ between SGA and AGA at the 2nd and the 6th week of life. However at 4 weeks a higher percentage of SGA neonates (42%) had MELTSH compared to AGA ones (24.7%, p<0.05). In the multivariate analysis it was found that, among the factors studied, being SGA is the only independent variable related with the presence of MELTSH (RR 2.8, CI 1.1–7.3).Conclusion: A high percentage of preterm neonates, especially in SGA, presents MELTSH at the first month of life but this finding is transient in most cases. Our results suggest that in preterm neonates with MELTSH and normal FT4, monitoring of TSH levels up to the second month of life is needed before the institution of replacement therapy.
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