Perimenopause, menopause and postmenopause are three stages of menopause, as per Cleveland Clinic. Perimenopause can begin 8-10 years before menopause and usually starts when a woman is in her 40s. Menopause is point when a person no longer has menstrual periods. Postmenopause comes after menopause. Women in this phase are at increased risk for osteoporosis due to low estrogen levels.