Understanding the Ovarian Clock - Essential Knowledge for Pediatricians.

A woman is born with her life-time supply of eggs, and these are surrounded by a group of cells, the follicular cells, which form the ovarian follicles. The ovarian follicles will determine a woman's entire reproductive lifespan (presence of menstrual cycles and length of fertility) and healthspan (i.e., quality of life). The ovarian follicles are at their peak numbers in utero and start to decline upon birth. This decline continues nonlinearly throughout the girls' growth to adolescence and in adulthood. This decline also represents the inevitable loss of fertility, culminating in women's menopause, where the ovaries have too few ovarian follicles left to result in monthly menstrual bleeding. The role of these ovarian follicles is vital for a woman's fertility as they safeguard the eggs within them. Importantly, the hormones secreted by the ovarian follicles (e.g., estradiol) maintain a woman's healthspan by ensuring optimal cardiovascular, musculoskeletal, and neurocognitive health. Conditions that accelerate the loss of these ovarian follicles or shorten the already limited ovarian lifespan will result in systemic issues detrimental to women's health. Yet, the biological processes that determine the ovarian clock remain understudied and this phenomenon needs attention to ensure that novel diagnostics and therapeutics are discovered for optimal women's reproductive health.