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 microg of gestodene and 15 microg 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 17beta-E2 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 17beta-E2 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.