The influence of the dose of ethinylestradiol in oral contraceptives on follicle growth

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Abstract
This prospective, randomized comparative clinical study involving 416 women investigated follicle development over a period of 12 oral contraceptive treatment cycles. Women were allocated to two groups, one group (n = 207) received a preparation containing 30 µg ethinylestradiol and 75 µg gestodene daily, and the other group (n = 209) received 20 µg ethinylestradiol and 150 µg desogestrel, daily. Follicular development was monitored by transvaginal ultrasonography of the ovaries, during days 18–21 in the pretreatment cycle and in treatment cycles 1, 3, 6, 9 and 12. Follicular development was found to be twice as frequent in the group receiving 20 µg ethinylestradiol/desogestrel as in the group receiving 30 µg ethinylestradiol/ gestodene. For all cycles, follicles of 10–30 mm were found in 18% of women in the desogestrel group, compared with 9.7% in the gestodene group, whilst follicles with a diameter of > 30 mm were present in 5% of the desogestrel group compared with 1.9% of the gestodene group. The difference between the treatment groups with respect to follicle diameters of 10–30 mm and > 30 mm was statistically significant (p < 0.05 and p < 0.001, respectively). No ruptured follicles were observed in either group throughout the study, suggesting that there was no escape ovulation, however, there was one pregnancy in the desogestrel group that could not be explained either by drug interactions or missed pills. It can be concluded that the ethinylestradiol dose in an oral contraceptive has a significant effect on follicular ovarian activity, and that reducing the dose to 20 µg is associated with a significant increase in follicle size.