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RAPID COMMUNICATION : A COMPARISON OF FREE T4 AND THE RATIO OF TOTAL T4 TO T4‐BINDING GLOBULIN IN SERUM THROUGH PREGNANCY

1982; Wiley; Volume: 17; Issue: 3 Linguagem: Inglês

10.1111/j.1365-2265.1982.tb01595.x

1365-2265

Amy Whitworth, J.E.M. Midgley, T A Wilkins,

Hypothalamic control of reproductive hormones

SUMMARY Serum free T4 concentrations have been variously reported as either constant or falling in pregnancy. In this study, 122 serum samples from apparently normal pregnancies were used to derive euthyroid ranges throughout pregnancy for T4 and free T 4 (measured by the Amerlex kits) and for T4‐binding globulin (TBG). The mean free T4 concentration fell with increasing gestational age, the range of values in the third trimester being narrower than the non‐pregnant normal range. Evidence is reviewed which shows that the Amerlex free T4 assay is unaffected by the elevation of TBG in non‐pregnant subjects. The decline in mean free T4 as pregnancy proceeds is in good agreement with the change in free T4 predicted by the falling T4/TBG ratio.