Thyroxine-binding by sera of pregnant women, new-born infants, and women - with spontaneous abortion

Among the many physiological alterations which may occur during pregnancy are thyromegaly (1), augmented thyroidal avidity for iodine (2, 3), and increase in the concentration of circulating thyroid hormone (4, 5). This triad of anatomical and functional alterations is ordinarily considered to be diagnostic of thyrotoxicosis. Paradoxically, however, these findings are neither accompanied by symptomatic stigmata of hyperthyroidism, nor are they associated, during the first half of preg-nancy, with increase in the basal metabolic rate. Although the basal metabolic rate increases dur-ing the latter half of pregnancy, this change has been ascribed by some to fetal needs, and not to alterations in maternal energy requirements (6). The origins and consequences of this unique functional dissociation are unknown. Recently there has been considerable interest in the physiological role and physicochemical prop-erties of the specific thyroxine-binding protein or proteins of plasma (TBP). Although the physio-logical role of TBP has not been elucidated, dem-onstration of this alpha globulin moiety in 1952 provided another parameter of thyroidal economy which is susceptible to measurement (7-11). Even earlier it had been suggested that the in-creased SPI of pregnancy might result from an alteration in the manner in which thyroxine in plasma is protein-bound (12, 13). Therefore, it appeared possible that study of the thyroxine