Reaching menopause is a gradual process of slowly decreasing hormones which may take years before the hormone production completely stops. This time of diminishing hormone levels causes changes throughout your body. The hormones produced by your ovaries affect many organs in your body, not just your reproductive organs. For example, ovarian hormones affect your skin, your cholesterol, your heart, your bones, your brain, your mood, and your intestinal tract, just to name a few. With this in mind, you can understand why your whole body experiences the loss of these hormones and why there are so many symptoms when they start to decrease.
Every woman experiences the hormonal changes prior to menopause differently.
When your level of hormones, specifically estrogen, become low enough it is safe to start on HRT if this is desired. This is a hormone that is produced by your brain in response to how much estrogen it is getting. The higher it gets, the less estrogen it is receiving. Generally, most labs consider an FSH above 20 to be high enough that it is safe to start estrogen therapy. When starting on HRT, you need to take estrogen and progesterone if you still have a uterus.