Growth rates of ovarian follicles during natural menstrual cycles, oral contraception cycles, and ovarian stimulation cycles.

OBJECTIVE: To compare growth rates of ovarian follicles during natural menstrual cycles, oral contraception (OC) cycles, and ovarian stimulation cycles using standardized techniques.
DESIGN: Prospective, comparative, observational, longitudinal study.
SETTING: Healthy volunteers in research trials and infertility patients undergoing treatment at an academic institution. PATIENT(S): Women were evaluated during natural cycles (n = 50), OC cycles (n = 71), and ovarian stimulation cycles (n = 131). INTERVENTION(S): Serial transvaginal ultrasonography was performed to measure follicle diameter. Day-to-day growth and regression profiles of individual follicles were determined. Mean growth rates were calculated for ovulatory follicles. Mean growth and regression rates were calculated for anovulatory follicles. MAIN OUTCOME MEASURE(S): Follicle growth rate (in millimeters per day). RESULT(S): Mean follicular growth rate was greater during ovarian stimulation cycles (1.69 +/- 0.03 mm/day) compared to natural (1.42 +/- 0.05 mm/day) and OC cycles (1.36 +/- 0.08 mm/day). The interval from dominant follicle selection to ovulation was shorter during stimulation cycles (5.08 +/- 0.07 days) compared to natural cycles (7.16 +/- 0.23 days). CONCLUSION(S): Follicles grew faster during ovarian stimulation therapy compared to natural cycles or OC cycles. Greater follicular growth rates in stimulation cycles were associated with shorter intervals from selection to ovulation. The biologic effects of increased follicular growth rates and shorter intervals to ovulation on oocyte competence in women undergoing assisted reproduction remain to be determined.