Initial and cyclic recruitment of ovarian follicles: a quarter-century update.

A review of advancements in primordial follicle activation and cyclic recruitment research over the past 25 years is presented. The review examines the latest insights into the mechanisms of primordial follicle activation and the role of the ovarian Hippo signalling pathways, highlighting their potential for developing new infertility treatments. The concept of continuous waves of early antral follicles and their availability for cyclic recruitment is discussed. Several previously unresolved questions, such as the effect of steroid contraceptive pill usage on menopause timing, the potential risk for earlier menopause in mothers of dizygotic twins and the effects of repeated ovarian stimulation cycles on menopause onset are addressed. Controversies about the existence of female germ stem cells, the lifespan of follicles, the phenomenon of alternate ovulation between ovaries, potential changes in menopause onset in patients with polycystic ovary syndrome (PCOS) and endometriosis are discussed. In conclusion, future challenges in ovarian research, aiming to advance understanding and improve clinical practices in reproductive health are addressed.