The menopausal transition is driven by fundamental changes in reproductive hormones. As the ovaries age and the number of egg-containing follicles diminishes, they produce less estrogen and progesterone, the primary hormones that control the menstrual cycle. In response to these falling estrogen levels, the pituitary gland in the brain releases higher amounts of Follicle-Stimulating Hormone (FSH) in an attempt to stimulate the ovaries to produce more estrogen. This is why an elevated FSH level is a key biological marker used to help confirm the menopausal transition. This profound hormonal shift, from a state of regular cycles to one of estrogen deficiency, is the root cause of most menopausal symptoms.