Perimenopause, also known as menopause transition, is a stage in a woman's reproductive life that occurs in the years just before she enters menopause. According to WebMD, this phase usually begins when a woman is in her 40s, but it can begin earlier.
Perimenopause lasts until a woman has not had a menstrual period for 12 months, at which time she enters menopause. According to the National Institute on Aging, the average age for a woman's final period, or menopause, is 51. During perimenopause, a woman's body begins to produce less estrogen, which makes her periods irregular and causes other menopause-like symptoms, including hot flashes, vaginal dryness, mood swings and a lowered sex drive.
Starting with perimenopause, the risk of osteoporosis and heart disease increases due to bone loss and rising cholesterol levels, according to the Mayo Clinic, which occur because of the declining amount of estrogen a woman's body produces during perimenopause. Women who go through perimenopause and menopause early have a higher risk of developing osteoporosis and heart disease than women who go through these phases later, according to the Mayo Clinic. These risks only increase further once a woman enters menopause and her estrogen levels decrease even further.