Effects on serum hormone levels of low-dose estrogen in place of placebo during the hormone-free interval of an oral contraceptive

BackgroundThe study was conducted to evaluate the effects of low-dose estrogen compared to placebo on ovarian activity during the traditional 7-day hormone-free interval (HFI) of an oral contraceptive (OC).Study DesignWomen were randomized to placebo or low-dose estrogen for 7 days during the HFI. Serum levels of estradiol, follicle-stimulating hormone (FSH), luteinizing hormone and inhibin B were obtained before, during and after treatment.ResultsMean hormone levels remained constant or only increased slightly for the low-dose estrogen group compared to greater more sustained increases observed for the placebo group. Estradiol, FSH and inhibin B levels were substantially higher for those on placebo. Differences were most noticeable by the end of the HFI and persisted into the subsequent cycle.ConclusionSubjects receiving low-dose estrogen for 7 days during the HFI demonstrated more pronounced ovarian suppression compared to placebo as evidenced by attenuation of increases in serum inhibin B, FSH and estradiol levels.