Background: Reports have described that, in adults, steroids suppress thyroid-stimulating hormone (TSH) and triiodothyronine (T3) and might suppress thyroxine (T4). No data have been reported for thyroid hormone changes before or after administration of glucocorticoid in preterm infants. Aims: The aim of this study was to investigate short-term effects of thyroid hormones on preterm infants. Index cases: We measured TSH, free T3 (FT3), and free T4 (FT4) before and after one or two doses of glucocorticoids administered to five infants at 29-37 weeks of corrected gestational age. Results: Comparison of thyroid hormone levels before and 1 day after glucocorticoid administration showed that TSH significantly decreased by 76% (64%-87%), FT3 by 33% (10%-50%), and FT4 by 10% (3%-17%). The decline in TSH and FT3 was followed by an increase around the pretreatment level at 3-15 days after glucocorticoid administration. In two of the five infants, FT4 continued to decrease from 1 day after glucocorticoid administration. Conclusions: In preterm infants, assessing thyroid hormones after glucocorticoid therapy demands caution because very short-term administration causes marked changes.
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