Summary
In 37 infants, the blood levels of TSH were determined by the immunoradiometric assay (IRMA) and the relation between TSH and thyroid hormone was evaluated. The ranges of gestational age (weeks) and birth weight (g) of jnfants were 28-42 and 982-3,650, respectively. The birth weights of 19 infants were below 2,500 g.
The free T4 levels in the low birth weight (LBW) infants were lower than those of the normal infants and significantly correlated to the birth weight (r=0.64, P < 0.01) and gestational age (r=0.58, P < 0.01). In addition, free T4 levels were significantly correlated to the levels of total T4 (r=0.66, P < 0.01). The concentrations of TSH measured by IRMA method were significantly correlated to those of free T4 (r=0.51, P < 0.01).
From these data, we consider that the transient hypo-thyroxinemia observed frequently in LBW infants might be a physiological reaction regulated by hypothalamus and that thyroid hormone treatment should be avoided.
Key-Words
Thyrotropin
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Thyroxine
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Free Thyroxine
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Low Birth Weight Infant
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Hypothyroxinemia
