Menopause, a woman’s permanent absence of menstruation, marks the end of women’s childbearing age. The average age of menopause for urban women in northern China is 49.5 years old, 47.5 years old for rural women, 48.99 years old for women in southern China and 51 years old for women in the United States. Most women usually go through a transitional period before menopause, medically known as perimenopause, or menopause. During this period, estrogen involved in regulating menstruation fluctuates, causing a series of climacteric symptoms, such as hot flashes and sleep disorders. Normal menstrual cycle For women of childbearing age, the periodic changes of estrogen and progesterone secreted by ovaries regulate the menstrual cycle of women: