Amenorrhoea is the absence of menstruation. It is a normal physiological event before puberty, during pregnancy, during lactation, and after the menopause.
Pathological amenorrhoea is the failure to menstruate for at least 6 months (or 6 cycles) during normal reproductive life in the absence of pregnancy. The extremes of reproductive age are set at 16 years - to allow for delayed menarche - and 40 years - the limit for premature menopause.
Patients with primary amenorrhoea have never menstruated; those with secondary amenorrhoea have had periods at some time in the past. Cryptomenorrhoea is used to describe women who are menstruating, but in whom bleeding is concealed, for example, because of an imperforate hymen.
Excluding pregnancy, about 20-30% of women experience amenorrhoea during reproductive life. The prevalence of amenorrhoea not due to pregnancy, lactation or menopause is estimated at 3-4% (1).