Abstract
Extract: Pituitary thyrotropic hormone (TSH) was measured in seven normal newborns followed during the first 72 hr of life. These infants demonstrated an acute unsustained release of TSH in the early minutes of postnatal life. Peak levels occurred between 15 and 150 min after birth, increasing from cord levels ranging from 3.2 10.7 μunits ml to a maximal elevation in sera of 25–163 μunits ml. This rise was followed by a steep decline in serum levels at an initial rate comparable to that reported for the half-life of the hormone. A slower rate of decay was noted after 120 min.
The TSH levels in 20 normal paired maternal and cord samples indicated that cord levels were consistently higher (t = 5.90, P < 0.001 ). Maternal levels were comparable to those found in nonpregnant adult females; however, cord levels of TSH were higher than that expected for normal children. Specificity of the TSH assay would indicate that immunoreactive TSH in maternal and cord sera was of pituitary origin.
Maternal thyroxine levels were significantly greater than those of cord sera (t = 3.31, P < 0.01), reflecting similarly higher levels of thyroxine-binding globulin (TBG) in maternal specimens (t = 7.31, P < 0.001). No significant differences (t = 1.11, P > 0.2) existed when levels of free thyroxine (FT.) in maternal and cord sera were compared.
Speculation: The relatively high levels of TSH in cord serum in the presence of normal or high normal free thyroxine concentrations would suggest that the hypothalamic-pituitary responsiveness to thyroxine in the fetus is altered. Free thyroxine concentrations that maintain TSH in the euthyroid range in normal children are apparently unable to do so in the fetus. Any other hypothesis for this observation must necessarily postulate a persistent stimulus to TSH secretion in utero. One such postulated stimulus could be a relatively low serum concentration of free triiodothyronine (T3) in the fetus.
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Czernichow, P., Greenberg, A., Tyson, J. et al. Thyroid Function Studied in Paired Maternal-Cord Sera and Sequential Observations of Thyrotropic Hormone Release during the First 72 Hours of Life. Pediatr Res 5, 53–58 (1971). https://doi.org/10.1203/00006450-197102000-00001
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DOI: https://doi.org/10.1203/00006450-197102000-00001
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