Abstract
Extract: Twenty-seven paired maternal-cord sera were analyzed for serum triiodothyronine (T3), total serum thyroxine (TT4), and maximum thyroxine globulin binding capacity (TBG cap.). In 17 of the infants the same studies were repeated at 1 week of age and in 10 of the 17 at 1 month. The mean T3 value for the cord sera was 73.1 ± 20.4 ng/100 ml while the mean value for the maternal sera was 204 ± 49.2. The difference in the mean values was highly significant (P < 0.001). The maternal T3 values are comparable with those of nonpregnant control subjects; those of cord blood fall below normal values. No statistically significant difference was found between the TT4 and TBG cap. values for cord and maternal sera. Both values were higher than the normal nonpregnant control values. At 1 week of age the serum T3 levels had increased to a mean of 208.4 ± 40.9 ng/100 ml. This mean is significantly different from the one observed in cord sera (P < 0.001). A significant increase in the TT4 values, mean 12.53 ± 2.2 μg/100 ml (P < 0.01), was observed by the end of the 1st week. TBG cap. did not change significantly between birth and 1 week of age; by the end of the 1st month of life the serum TT4 had decreased significantly to a mean of 9.5 ± 2.7 μg/100 ml (P < 0.05), while the serum T3 was maintained at a mean level of 228.2 ± 16.9 ng/100 ml, a value not significantly different from the one observed at 1 week of age.
Speculation: The extremely low levels of T3 in the cord blood in the presence of TT4 and TBG cap. values equal to those of the maternal blood suggest minimal materno-fetal placental transfer of T3. We have postulated that the low fetal T3 is responsible for the high levels of pituitary thyrotropic hormone (TSH) present in cord blood and early in the postnatal period and that the high levels of TT4 with normal T3 levels observed by the end of the 1st week of life indicate defective peripheral deiodination of thyroxine (T4) to T3 and account for the lack of signs and symptoms of hyperthyroidism. By the end of 1 month of age TT4 and T3 values are within normal ranges, which indicates maturation in the metabolic pathway of T4 and T3.
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Montalvo, J., Wahner, H., Mayberry, W. et al. Serum Triiodothyronine, Total Thyroxine, and Thyroxine to Triiodothyronine Ratios in Paired Maternal-Cord Sera and at One Week and One Month of Age. Pediatr Res 7, 706–711 (1973). https://doi.org/10.1203/00006450-197308000-00006
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DOI: https://doi.org/10.1203/00006450-197308000-00006