Pre-menopause is the natural transition period towards menopause, when the ovarian reserve starts to decrease and a woman loses her fertility. It usually begins around the age of 40 and lasts for a very variable period of time, from a few years to 10 years or more.
On the other hand, perimenopause is a shorter stage that precedes menopause and lasts until 12 months after the last menstruation. It usually lasts about 2 or 3 years and is characterized by irregularities in the menstrual cycle. The most common age of perimenopause is between 45 and 50 years old.