The term natural menopause defines the permanent cessation of menstruation resulting from the loss of ovarian activity. Menopause or the final menstrual period can only be determined retrospectively, after at least 12 months without periods.
Average age at the menopause is currently around 50 years in Western industrialized societies (in Britain it is 50.78 and in the United States 49.8). Premature menopause is defined as the final menstrual period occurring before the age of 40 years. In addition to race (menopause occurs earlier in black women), nutrition and smoking influence the age at the menopause. It has been suggested that age at menopause may be a biological marker of aging, i.e. later menopausal age being associated with longevity.
The peri-menopause refers to the period immediately prior to the menopause, during which there is clinical and hormonal evidence of impending menopause, and to the first year after the last menstrual period. At about the age of 40 menstrual cycles tend to become irregular and anovulatory cycles are more frequent. This is characteristic of the peri-menopause which can last for some time, on average about five years. Although some women may claim that their menses ceased abruptly after “having always been regular” this is rare since a pre-menopausal phase of less than one year occurs in only 1% of the women. This phase is also referred to as “menopausal transition” and is generally associated with the onset of typical menopausal symptoms, most often “psychosomatic”, such as irritability, nervousness, depression, disturbed sleep, headache and fatigue. The vasomotor flush, the hallmark of the menopausal transition, is frequently first manifested at that time.
The term post-menopause defines the phase after the final menstrual period. The term pre-menopause refers to the whole of the reproductive period prior to the menopause.