Effects of oral contraceptives administered at defined stages of ovarian follicular development

To elucidate the effects of initiating oral contraceptives (OC) at defined stages of ovarian follicle development. Prospective longitudinal study. Healthy volunteers in an academic research environment. Forty-five healthy women between the ages of 18 and 35 years, randomized to initiate OC when a follicle diameter of 10, 14, or 18 mm was first detected. The OC administration at defined stages of dominant follicle development. Fates of all dominant follicles and serum concentrations of E 2-17β, LH, and P before and after initiating OC. No ovulations (0/16) were observed when OC use was initiated at a follicle diameter of 10 mm, 4/14 (29%) follicles ovulated when OC were initiated at 14 mm, and 14/15 (93%) ovulated when OC were initiated at 18 mm. When ovulation did not occur, follicles regressed or became anovulatory cysts. Peak LH and E 2 levels were lowest in the 10-mm group, moderate in the 14-mm group, and greatest in the 18-mm group. Peak endocrine levels in all treatment groups were lower than the historic reference group. Follicular development, ovulation, and endocrine concentrations were not suppressed effectively when OC were initiated at late stages of dominant follicle development.