Amenorrhoea - the absence of periods (menstruation), which also means no eggs are produced (anovulation). In many cases, as in girls before puberty, or during pregnancy, breastfeeding or the menopause, this is normal and is called physiological amenorrhoea. An associated condition known as Oligomenorrhoea refers to infrequent periods, usually every three to six months which may be irregular and long.

Primary amenorrhoea is the failure to establish menstruation. It is regarded as abnormal if a girl has not started sexual physical development and menstruation by the age of 14, or if a girl with normal sexual physical characteristics has not started menstruation by the age of 16. Primary amenorrhoea affects only about 3 girls per 1000.

Secondary amenorrhoea is defined as the absence of menstruation for six consecutive months in a woman who previously had regular periods. Secondary amenorrhoea implies a gynaecological disorder or a general cause or disease.

Secondary amenorrhoea affects about 3% of girls. Up to 50% of competitive long-distance runners (running 80 miles per week) and up to 44% of ballet dancers have amenorrhoea.

Causes

There are many possible causes. They include:

• Excessive exercise. It is particularly common in athletes involved in endurance events.
• Being severely underweight, as a result of an eating disorder or illness. Regular menstruation is unlikely if the body mass index (weight in Kg divided by the height in metres squared) is less than 19 (the normal range is 20 to 25).
• Severe stress or emotional disturbance
• A disorder of the ovary that prevents eggs from being produced
• Various medical drugs
• A reaction to stopping the contraceptive pill. About one woman in 100 will have amenorrhoea for three to six months after stopping use of the pill. This is commonest in women who have taken the pill continuously without a regular pill-free interval.
• Polycystic ovary syndrome: a condition associated with multiple cysts in the ovaries, which features menstrual disturbances or absence of menstruation, sterility, obesity and a male distribution of body hair from hormonal disturbances. Severe long-term illness, or under- or over-activity of the thyroid gland.
• Abnormal operation of the hormones controlling ovulation and menstruation produced by the hypothalamus gland (which in turn controls the pituitary gland).

Rare causes of amenorrhoea include:

• Absence at birth of the vagina, or womb, or both
• A hymen that completely closes off the vagina

There are rare cases where the true sex of a child is confused because of poorly developed genital organs at birth.