Ovarian activity suppression by two different low-dose triphasic oral contraceptives

In an open, randomized study in an outpatient clinic of a large teaching hospital, thirty-one female volunteers with regular cycles and established ovulation by ultrasonography were given one of two triphasic oral contraceptives containing ethinylestradiol combined with levonorgestrel or desogestrel during six cycles of treatment. The main outcome measures were transvaginal ultrasonography and serum E2 and P measurements in pill cycles 1, 3 and 6. No ovarian activity was found in 10 subjects. Among the remaining 21 women who showed ovarian activity, most follicle-like structures developed in the pill-free week and decreased in size or disappeared in the first pill week. One women taking triphasic desogestrel had evidence of a luteinized unruptured follicle and one women taking triphasic levonorgestrel had a possible ovulation. The latter women also showed symptoms of lower abdominal pain. A statistically significant difference in ovarian activity between the two oral contraceptives could not be established. The two triphasic oral contraceptives suppressed ovarian activity to the same degree. A trend was seen towards increasing ovarian activity with duration of use in both treatment groups.