THYROID-FUNCTION IN EARLY NORMAL-PREGNANCY - TRANSIENT SUPPRESSION OFTHYROID-STIMULATING HORMONE AND STIMULATION OF TRIIODOTHYRONINE

In order to determine the effect of gestation on thyroid function in h ealthy subjects, we have prospectively evaluated thyroid function in p regnant individuals undergoing termination of pregnancy, and repeated the tests 2-3 months later. Venous blood was tested for human chorioni c gonadotropin (hCG), thyroid-stimulating hormone (TSH), free thyroxin e (FT4) and total triiodothyronine (TT3). Early pregnancy thyroid func tion tests showed a significant decrease (p < 0.001) in TSH and a sign ificant increase (p < 0.001) in TT3 as compared to the nonpregnant sta te; FT4, however, did not change significantly. In 8 (11.2%) pregnant subjects, TT3 levels were above the normal range for nonpregnant contr ols. Elevated thyroid function in early pregnancy is transient, and do es not usually warrant antithyroid treatment. Thus, any conclusion reg arding thyroid function in early pregnancy should be based on pregnant controls rather than general population controls.