Perimenopause, also known as menopausal transition, is the period of time before menopause when a woman's body gradually begins to produce less estrogen. Perimenopause typically starts in a woman's 40s but can start as early as her 30s. During perimenopause, women may experience changes in their menstrual cycle, including irregular periods, heavier or lighter bleeding, or missed periods. Women may also experience symptoms similar to those of menopause, such as hot flashes, mood changes, and sleep disturbances. Perimenopause can last several years and ends when a woman has gone 12 consecutive months without a menstrual period, marking the onset of menopause.