Assessment of thyroid status in pregnant women and in patients taking oral contraceptives by a free thyroxine index.

The results of using a product of serum thyroxine and triiodothyronine binding coefficient, estimated by simple methods, to give a ;free thyroxine index' in normal women, in pregnant women, and in patients taking oral contraceptives is described. The method is believed to provide a reliable means of assessing thyroid status, and very close agreement, with no significant difference between the mean values obtained for the free thyroxine index, was found in the groups studied. Certain changes, which may be significant, in the values obtained in patients on oral contraceptive treatment of varying duration were noted.