Predicting risk of ovulation in new start oral contraceptive users

OBJECTIVE: To assess ovarian follicular development and ovulation rates in women starting to take oral contraceptives (OC) on menstrual cycle day 1, 4, or 7. METHODS: One hundred thirty women starting treatment with OC were randomized to begin use of ethinyl estradiol, 30 μg, plus norgestrel, 300 μg, on menstrual cycle day 1 (group 1), 4 (group 2), or 7 (group 3). Follicular development was assessed by vaginal ultrasonography on menstrual cycle days 7, 14, 21, and 28, and serum progesterone levels were measured on menstrual cycle days 21 and 28. At a .05 level of significance (two-tailed) and power of 80%, 84 participants were required to complete the study. Eighty-five women who met study criteria, made minimal dosing errors, and underwent at least three ultrasonographic examinations were analyzed. RESULTS: A follicle-like structure that reached a maximum diameter over 13 mm was observed in three of 29 (10.3%), five of 29 (17.2%), and 12 of 27 (44.4%) women in groups 1, 2 and 3, respectively (P = 0.003). The median maximum follicle size for each group was 9.0 mm, 9.0 mm, and 12.0 mm for start day 1, 4, and 7 respectively (P < .001). Evidence of ovulation based on serum progesterone was present in two, one, and zero women in groups 1, 2, and 3, respectively (P = .2). CONCLUSION: Although a delay in oral contraceptive initiation results in significantly more ovarian follicular development, the postponement does not appear to increase actual ovulation rates.