Effects of an oral contraceptive containing 30 mcg ethinyl estradiol and 2 mg dienogest on thyroid hormones and androgen parameters: conventional vs. extended-cycle use

BackgroundThis study was conducted to investigate the effects of an oral contraceptive containing 30 mcg ethinyl estradiol and 2 mg dienogest on thyroid hormones and androgen parameters.Study designThyroid and androgen parameters were measured in 59 women treated with a monophasic combined oral contraceptive containing 30 mcg ethinyl estradiol and 2 mg dienogest (EE/DNG) either conventionally (13 cycles with 21 days of treatment+7 days without hormones) or according to an extended-cycle regimen (four extended cycles with 84 days of continuous administration of EE/DNG, followed by a hormone-free interval of 7 days). Blood samples were taken on Days 21–26 of the preceding control cycle and on Days 19–21 of the 3rd and 13th conventional cycle, or on Days 82–84 of the first and fourth extended cycle.ResultsAt both time points, the serum concentrations of thyroxine-binding globulin were elevated by about 65% in both treatment regimens. Likewise, both groups showed an increase in total triiodothyronine (T3) and total thyroxine (T4) by 30–40%, and no change in free T4. Until the 12th month of conventional treatment, the level of free T3 remained unchanged but decreased slightly during the extended-cycle regimen. In both groups there was a rise of sex hormone-binding globulin by 210–230% after 3 months and by 220–250% after 12 months. The levels of total testosterone were reduced by about 40% and those of free testosterone by 55–65% after 3 and 12 months.ConclusionThe results suggest that, during conventional and extended-cycle treatment with EE/DNG, a steady state in the effects on thyroid hormones and androgen parameters was reached within 3 months and that the changes in the various hormonal parameters did not substantially differ between conventional and extended-cycle regimen.