Ovarian antral folliculogenesis during the human menstrual cycle: a review.

BACKGROUND Ovarian follicles undergo dynamic morphologic and endocrinologic changes during the human menstrual cycle. The physiologic mechanisms underlying recruitment and selection of antral follicles in women are not fully elucidated. METHODS A comprehensive review of >200 studies was conducted using PubMed. The objective was to compare and contrast different perspectives on human antral folliculogenesis. RESULTS Antral folliculogenesis has been studied using histologic, endocrinologic and/or ultrasonographic techniques. Different theories of antral follicle recruitment include: (i) continuous recruitment throughout the menstrual cycle; (ii) recruitment of a 'cohort' of antral follicles once in the late-luteal phase or early-follicular phase of each cycle and (iii) recruitment of two or three 'cohorts' or 'waves'  during each cycle. Generally, a single dominant follicle is selected in the mid-follicular phase of each cycle and this follicle ovulates at mid-cycle. However, a dominant follicle may also be selected during anovulatory waves that precede the ovulatory wave in some women. CONCLUSIONS There is increasing evidence to indicate that multiple waves of antral follicles develop during the human menstrual cycle. Ovarian follicular waves in women are comparable with those documented in several animal species; however, species-specific differences exist. Enhancing our understanding of the endocrine and paracrine mechanisms underlying antral follicular wave dynamics has clinical implications for understanding age-related changes in reproductive function, optimizing hormonal contraceptive and ovarian stimulation regimens and identifying non-invasive markers of the physiologic status of follicles which are predictive of oocyte competence and assisted reproduction outcomes.