Effect of 21-day and 24-day oral contraceptive regimens containing gestodene (60 μg) and ethinyl estradiol (15 μg) on ovarian activity

Objective: To compare ovulation inhibition and ovarian activity with 21-day and 24-day regimens of a low-dose combined oral contraceptive (COC) containing 60 μg of gestodene and 15 μg of ethinyl estradiol. Design: Interventional observational study. Setting: Reproductive medicine unit. Patient(s): Fifty-eight healthy volunteers aged 18–35 years. Intervention(s): Ovarian activity was monitored every other day with the use of ultrasound to measure the diameters of follicle-like structures and blood samples to measure serum concentrations of 17β-E 2 and progesterone. Subjects were observed for five cycles: pretreatment and posttreatment control cycles and three cycles in which the COC was administered for either 21 or 24 days of each cycle. Main Outcome Measure(s): Occurrence of ovulation and evidence of ovarian activity. Result(s): The study was completed by 27 (90%) of the 30 subjects who received the 24-day regimen and by 24 (79%) of the 28 subjects who received the 21-day regimen. Ovulation was inhibited in all cycles in the 24-day group and in 74 of 75 cycles in the 21-day group. Luteinized unruptured follicles were seen in no cycles with the 24-day regimen and in 6 (8%) of 75 cycles with the 21-day regimen. Mean ovarian follicular development and serum 17β-E 2 and progesterone levels were lower in the 24-day group. Conclusion(s): The 24-day regimen is an innovative strategy for maintaining effective ovulation inhibition at ultra-low doses of contraceptive steroids.