Perimenopause refers to the time during which your body makes the natural transition to menopause, marking the end of the reproductive years. The level of estrogen in your body rises and falls unevenly during this period. Your menstrual cycles may lengthen or shorten, and you may begin having menstrual cycles in which your ovaries don’t release an egg. You may also experience menopause-like symptoms, such as hot flashes, sleep problems, and vaginal dryness.