Menopause reflects the end of ovarian activity which leads to a marked reduction in circulating levels of the hormone, oestrogen.
The average age of the menopause is 51. If menopause occurs between 40 and 45, this is considered an early menopause. If menopause occurs before 40, this is known as premature menopause, also termed premature ovarian insufficiency (POI).
The most obvious sign that ovarian activity has ended is that menstrual periods stop. A woman is said to be post-menopausal if she has not had any periods for 12 months. Stoppage of periods does not happen overnight. The transition occurs gradually over years, usually beginning after age 45. This transitional phase is referred to as the perimenopause. During the perimenopause, periods become more and more irregular and increasingly spread apart, often separated by 2 or more months. Other signs of oestrogen deficiency are also apparent during this time, especially hot flushes and night sweats which are known as vasomotor symptoms.