Pre and post-menopausal questions come up as women have symptoms and their period cycle changes. Pre-menopause (also known as perimenopause) generally occurs for women between 40 and 55 years old, but it can occur earlier. The average age for women in the United States is 52 to enter menopause. During pre-menopause, estrogen levels rise and fall unevenly. This can result in irregular periods, hot flashes, and vaginal dryness, trouble sleeping, which can last for several years until periods stop. Perimenopause ends when a person goes for 12 months without a period. A person is considered post-menopausal after they have not had a period for more than 12 months.