Abstract
The clinical value of free thyroxine index, thyroxine/thyroxine binding globulin ratio, and free thyroxine concentration were compared in 46 pregnant patients. Overall the free thyroxine index was the best diagnostic index. Pregnancy induced changes in levels of free thyroxine and the thyroxine/thyroxine binding globulin ratio, which gave rise to interpretative problems in some pregnant subjects.