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In the female reproductive system, the menstrual cycle is a recurring cycle of physiologic changes that occurs in reproductive-age females. Overt menstruation (where there is blood flow from the vagina) occurs primarily in humans. Menstruation is a common thing that happens to every woman when puberty. Some women never go through puberty, so periods never start. This disorder is called primary amenorrhea. In other women, periods start at puberty, then stop. This disorder is called secondary amenorrhea. Amenorrhea is normal only before puberty, during pregnancy, while breastfeeding, and after menopause.

Amenorrhoea is a symptom with many potential causes. Primary amenorrhoea (menstruation cycles never starting) is the absence of menstruation in a woman by the age of 16. It may be caused by developmental problems such as the congenital absence of the uterus, or failure of the ovary to receive or maintain egg cells. Also, delay in pubertal development will lead to primary amenorrhoea. Primary amenorrhea may be caused by a birth defect in which the uterus or fallopian tubes do not develop normally or by a chromosomal disorder, such as Turner syndrome (in which the cells contain one X chromosome instead of the usual two). Primary amenorrhea can also result from malfunction of the hypothalamus (a part of the brain), pituitary gland, or ovaries. Sometimes it results from malfunction of the thyroid gland (hyperthyroidism or hypothyroidism). Young women who are very thin, particularly those who have anorexia nervosa, may never menstruate.

Secondary amenorrhoea (menstruation cycles ceasing) is often caused by hormonal disturbances from the hypothalamus and the pituitary gland or from premature menopause, or intrauterine scar formation. Secondary amenorrhea can result from malfunction of the hypothalamus, pituitary gland, ovaries, thyroid gland, adrenal glands, or almost any part of the reproductive tract. Malfunction of these organs may result from a tumor, an autoimmune disorder, or use of certain drugs (including hallucinogenic drugs, chemotherapy drugs, antipsychotic drugs, and antidepressants). Cushing’s syndrome and polycystic ovary syndrome (both of which involve hormonal abnormalities) may cause periods to stop or to be irregular. Other causes of secondary amenorrhea include a hydatidiform mole (a tumor that develops from an abnormal fertilized egg or the placenta) and Asherman’s syndrome (scarring of the lining of the uterus resulting from an infection or surgery).

Stress due to internal or situational concerns can cause secondary amenorrhea, because stress interferes with the brain’s control (through hormones) of the ovaries. Exercising too much or eating too little (as in anorexia nervosa) also affects the brain’s control of the ovaries. Either behavior can cause the brain to signal the pituitary gland to decrease its production of the hormones that stimulate the ovaries. As a result, the ovaries produce less estrogen and periods stop.

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