We presented data showing a direct correlation of screening T4 values with birthweight in premature infants at this meeting three years ago.We opined that low T4 concentrations were due to decreased protein binding of T4. The next year,we reported data proving the speculation and showing lower binding was more than compensated for in term infants by increased TBG concentration. FT4 concentrations for term and VLBW infants were all within the normal adult range and the neonates had similar TSH concentrations indicating low T4 values were due to NTI. Further findings at 2 weeks in 5 of 32 VLBW infants suggest a Euthyroid Sick Syndrome. We compare clinical and hormonal values of these 5 with the remaining 27 infants in the tables.(cord v 2 wk- * p <.05 ** <.01) The FT4 method was validated by equilibrium dialysis.The correlation of immaturity and postnatal stress with the hormonal changes was also demonstrated by regression analyses. The values became normal in 3 of the 4 infants followed for 4 weeks. We believe the changes in hormonal values are due to a transient inhibitor of T4 binding unrelated to the diminished binding seen in both VLBW and term infants previously demonstrated. The putative transient inhibitor is associated with immaturity and stress.

Table 1
Full size table