What is Perimenopause / Menopause? According to The Centre for Menstrual Cycle and Ovulation Research, menopause is a time in a woman’s life with no period for 12 months. The average age of menopause is 51. The stage prior to menopause is called perimenopause. During perimenopause, women have changes in their monthly menstrual cycle, mood, hot flashes, brain fog and more. Perimenopause can start between the mid-30s and the late 40s. The average age at which irregular cycles develop is approximately age 47. Perimenopause begins in women with regular cycles whose ovaries then begin producing less hormones, often causing your menstrual cycle to become erratic or irregular. During perimenopause, women typically are making higher amounts of estrogen compared to significant low levels of progesterone. The low levels of progesterone compared to substantially high estrogen makes perimenopause the most difficult time for all women. In contrast to Menopause, both estrogen and progesterone levels normally become low and remain low throughout the remainder of life. Hot flashes can occur in both perimenopause and menopause. Perimenopause can last about 7 years and in some cases up to 14 years. During this time, higher estrogen causes weight gain through insulin resistance and by increased body fat. Higher insulin levels cause increased appetite and weight gain. Perimenopause also causes weight gain as progesterone levels are too low. Progesterone, responsible for raising the basal temperature during the second half of the ovulatory menstrual cycle, makes us burn about 300 extra calories a day. Without progesterone, we don't burn these extra calories and instead store the extra energy.