1268 A LONGITUDINAL ASSESSMENT OF THYROID FUNCTION IN THE VERY LOW BIRTHWEIGHT (VLBW) INFANT

Abstract

Assays of serum T3, T4 and TSH were performed on cord blood & then serially at 3, 24 and 72 hrs; at 1 week and weekly until 6 wks in 11 VLBW infants(<1200gm). In response to parturition,there was a TSH surge (cord 7.1 ± 3.6mu/ml; 3 hrs 8.7 ± 5.lmu/ml) and elevation of T4(cord 7.1 ± 1.8μg/dl; 3 hrs 9.3 ± 3.6μg/dl). TSH then fell to a nadir at 72 hrs(2.1 ± 1.Omu/ml); T4 at 3 wks(4.1 ± 2.3 μg/dl). Subsequently T4 increased; at 6 wks(5.3 ± 2.7μg/dl). T3 closely paralleled T4 with a nadir at 2 wks of 66.1 ± 36.2ng/dl, rising to 106.9 ± 22.0 at 5 wks. Analysis of data revealed significantly lower(p<.05)T4 in infants with RDS(n=5)vs those without RDS(n=6)at 24 and 72 hrs as well as at wks 1, 2, 3 and 6. T3 and TSH were not significantly different in these groups. Comparison of survivors(n=8)vs non-survivors(n=3)revealed significantly lower T4 in the latter at 3 hrs(p<.05), 2 wks(p<.005), 3 wks(p<.005) and 4 wks(p<.05). T3 and TSH were not statistically different. These normative data are in general agreement with previously reported values in larger preterm infants, reflecting the pattern in fullterm infants albeit of a significantly less degree. No treatment is recommended for preterm infants with low T4 since these values increase to normal over several weeks. Reassessment of this recommendation seems warranted in light of the above which indicates some of these infants do not recover; their relative hypothyroid state may not be a physiologic responce to their illness but significantly related to morbidity and mortality.

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