Menopause denotes the cessation of menstruation in women, which usually occurs when a woman reaches the age of fifty but may occur as early as 40 and as late as 55 years of age. Six to twelve months without a menstrual period is the commonly accepted rule for diagnosing menopause. The time period prior to menopause is referred to as perimenopausal, while the time period after menopause is referred to as postmenopausal. During the perimenopausal period, many women have irregular periods.