The regulation and assessment of follicular growth

Folliculogenesis is the process by which waves of small primordial follicles possessing immature oocytes are recruited to undergo development into large antral follicles, with one then being selected for ovulation of a fully competent oocyte. Folliculogenesis can be divided into three stages: follicle recruitment, selection and ovulation, and has two phases: the initial gonadotrophin-independent phase and the later gonadotrophin-dependent phase. It involves an elaborate array of biochemical signalling factors, both stimulatory and inhibitory, and the regulation of follicle growth relies on these being tightly controlled. Their increasing understanding allows reproductive biologists to attempt manipulation of folliculogenesis, which can be useful in clinical areas such as assisted reproduction and contraception. The rising average age of childbearing in many developed countries is bringing an additional focus on the importance of assessing a woman's non-growing follicular pool; i.e. her ovarian reserve. This review examines the important regulatory players in the different stages of folliculogenesis and describes some of the currently available measures of ovarian reserve.