Thyroid function during treatment with a new oral contraceptive combination containing desogestrel

Abstract

The present study was carried out to assess the effect of an oral contraceptive combination containing 0.075 mg desogestrel (Org 2969, 17 alpha-ethinyl-18-methyl-11-methylene-4-estren-17-ol) plus 0.050 mg ethinyloestradiol on thyroid function in healthy women. All 15 volunteers participated for three cycles; in each cycle they took 1 tablet daily for 21 consecutive days, followed by a 17-day tablet-free period. In total, 'treatment' lasted 3 months. After 3 months treatment serum thyroxine significantly increased (+ 43.9%), as did free thyroxine index (+ 20.0%) and thyroxine-binding globulin (+ 101%). Serum triiodothyronine uptake to Sephadex decreased (- 17.3%), corresponding to the decrease in thyroxine/thyroxine-binding globulin ratio (- 23.8%). Serum triiodothyronine and thyrotropin (TSH) concentrations did not change. After treatment had stopped, all values rapidly returned to initial levels. As a more specific parameter of thyroid function, serum free thyroxine concentration was measured. During treatment a slight decrease of - 125% (which was within normal limits) was observed. Moreover, the pituitary response to TSH-releasing hormone (TRH) was not changed. Thus, treatment with desogestrel plus ethinyloestradiol in the present combination did not alter thyroid function.