Manipulation of the pill-free interval in oral contraceptive pill users: The effect on follicular suppression

Objective: The purpose of this study was to compare follicular suppression that was produced by 3 different oral contraceptive regimens that differ by treatment in the pill-free interval. Study design: In a university setting, 54 women were assigned randomly to receive either 20 μg ethinyl estradiol + 100 μg levonorgestrel followed by 7 pill-free days, 20 μg ethinyl estradiol + 150 μg desogestrel followed by 2 days of placebo then 10 μg ethinyl estradiol for 5 days, or 28 days of 20 μg ethinyl estradiol plus 150 μg desogestrel. Follicular suppression was evaluated by serial ultrasound scans and by serum and urinary hormone levels during a 2-month study period. Data were analyzed by nonparametric statistical tests. Results: There was a significant difference in follicle count among the 3 groups (P = .005). Women who were treated with a 7-day pill-free interval experienced the least suppression. Estrogen levels were more variable and led to an observation that overweight (body mass index, > 25 kg/m²) was associated with reduced follicle suppression (relative risk, 1.6; 95% CI, 1.0, 2.7) and higher estrogen levels (relative risk, 5.3; 95% CI, 1.3, 21). Conclusion: Contraceptive pill users who were treated with a 7-day pill-free interval demonstrated less follicular suppression than women who were supplemented with either estrogen alone or estrogen plus progestin. Overweight women were less suppressed than women of normal weight.