THE INFLUENCE OF THE DOSE OF ETHINYLESTRADIOL IN ORAL-CONTRACEPTIVES ON FOLLICLE GROWTH

This prospective, randomized comparative clinical study involving 416 women ir investigated follicle development over a period of 12 oval co ntraceptive treatment cycles. Women were allocated to two groups, one group (n = 207) received a preparation containing 30 mu g ethinylestra diol and 75 mu g gestodene daily, and the other group (n = 209) receiv ed 20 mu g ethinylestradiol and 150 mu g desogestrel, daily. Follicula r development was monitored by transvaginal ultrasonography of the ova ries, during days 18-21 in the pretreatment cycle and in treatment cyc les 1, 3, 6, 9 and 12. Follicular development was found to be twice as frequent in the group receiving 20 mu g ethinylestradiol/desogestrel as in the group receiving 30 mu g ethinylestradiol/gestodene. For all cycles, follicles of 10-30 30 mm were found in 18% of women in the des ogestrel group, compared with 9.7% in the gestodene group, whilst foll icles with a diameter of > 30 mm were present in 5% of the desogestrel group compared with 1.9% of the gestodene group The difference betwee n 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, res pectively). No ruptured follicles were observed in either group throug hout the study, suggesting that there was no escape ovulation, however , there was one pregnancy in the desogestrel group that could not be e xplained either by drug interactions or missed pills. It can be conclu ded that the ethinylestradiol dose in an oval contraceptive has a sign ificant effect on follicular ovarian activity, and that reducing the d ose to 20 mu g is associated with a significant increase in follicle s ize.