Figure 1. Schematic representation of human ovarian follicle development. Primordial follicles entering the growth phase form primary follicles (class 1). This is followed by gonadotropin-independent (tonic) growth (class 1 to 4), and eventually gonadotropin (Gn)-dependent growth. Note that the overall development from a class 1 to a class 5 follicle takes three cycles [Reproduced with permission from A. Gougeon].
Source: Endocr Rev 1997 Feb;18(1):71-106
Edited by Aldo Campana,