There are three stages of menopause that experts creatively (not) call perimenopause (the period before), menopause (during), and postmenopause (after). Perimenopause normally begins around the age of 40 when the ovaries produce less and less estrogen. It can last for around 10 years. And it’s the last couple of years of perimenopause that are associated with those pesky hot flashes, disturbed sleep, and other uncomfortable symptoms. A woman becomes postmenopausal when she has not had her period for a year.