Abstract
Paired arterial and venous cord blood samples were obtained from 29 normal newbrons (15 M & 14 F). T4 & TBG were determined for all and additionally other indices were determined as follows T3 in 27 (14 M & 13 F), RT3 in 16 (8 M & 8 F), thyroglobulin (Tg) in 14 (7 M & 7 F) and TSH in 11 (5 M & 6 F).
No sex difference in thyroid indices was found. Arterial and venous cord serum thyroid indices correlated positively (T4, r=0.673, TBG, r=0.752, T3, r=0.909, RT3, r=0.913, Tg, r=0.934, & TSH, r=0.989, p < 0.005). The differences between the means ± SD of arterial and venous levels was significant (p < 0.05) only for RT3 (203 ± 43.3 vs 237 ± 61 ng/dl). Arterial (T4 vs T3, r=0.451 p < 0.01 & T4 vs RT3, r=0.566, p < 0.025) and venous (T4 vs T3, r=0.627, p < 0.005 & T4 vs RT3, r=0.628, p < 0.005) T3 and RT3 levels correlated positively with T4 levels. In contrast, arterial (r=0.104, p>0.3) and venous (r=0.115, p>0.3) T3 and RT3 levels did not correlate significantly.
These data are in keeping with the reports that suggest that placental inner ring deiodination of maternal thyroxine is a source of fetal RT3. The findings support the suggestion that placental inner ring deiodination of T4 and T3 may be the mechanism responsible for the failure of maternal T4 and T3 to cross the placenta.
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Penny, R., Sims, M., Campbell, W. et al. 9 Reverse Triiodothyronine (RT3) Levels In Paired Arterial And Venous Cord Blood Are Consistent With Greater Inner Ring Deiodoination of Thyroxine (T4) On The Venous Side. Pediatr Res 19, 605 (1985). https://doi.org/10.1203/00006450-198506000-00029
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DOI: https://doi.org/10.1203/00006450-198506000-00029