Perimenopause means "around menopause" and refers to the time period during which a woman's body makes its natural transition toward permanent infertility (menopause). Perimenopause is also called the menopausal transition.
Women start perimenopause at different ages. You may notice signs of progression toward menopause, such as menstrual irregularity, sometime in your 40s. But some women notice changes as early as their mid-30s.
The level of your estrogen — the main female hormone — rises and falls unevenly during perimenopause. Your menstrual cycles may lengthen or shorten, and you may begin having menstrual cycles in which your ovaries don't release an egg (ovulate). You may also experience menopause-like symptoms, such as hot flashes, sleep problems and vaginal dryness. Treatments are available to help ease these symptoms.
Once you've gone through 12 consecutive months without a menstrual period, you've officially reached menopause, and the perimenopause period is over.