Follicular development and apoptosis.

More than 99.9% of the ovarian follicles present at birth never reach ovulation. The most common fate of follicles is instead to undergo atresia, which has been shown to be mediated by a highly organised type of cell death called apoptosis or programmed cell death (Hsueh et al. 1994; Billig et al. 1996; Kaipia and Hsueh 1997). The final tuning of the large number of growing follicles to a single ovulatory follicle is primarily achieved by cell death of granulosa cells (Hsueh et al. 1994; Reynaud and Driancourt 2000).