Figure 1.The timetable of normal folliculogenesis in women. Class 1: the preantral or gonadotropin-independent period. It takes ~290 days for a recruited primordial follicle to grow to a fully-grown secondary follicle. Class 3-8: the antral (Graafian) or gonadotropin-dependent period. From cavitation or beginning antrum formation, it takes ~60 days to pass through the small (Class 2-4) medium (Class 5, 6) and large (Class 7) and preovulatory (stage 8) Graafian follicle stages. A dominant follicle is selected from a cohort of class 5 follicles. Once selected, it requires ~20 days for a dominant follicle to reach the ovulatory stage. Atresia can occur in developing follicles after the secondary stage. Number of granulosa cells (gc); days (d). (Gougeon A: Dynamics of follicular growth in the human: A model from preliminary results. Hum Reprod 1:81, 1986. Reproduced with permission from Oxford University Press.)