Abnormal absence of menstrual periods is called amenorrhea. Amenorrhea is normal in girls before puberty and in women during pregnancy, while breastfeeding, and after menopause. The absence of menstrual periods when periods are normally expected, however, is an abnormal condition.
Amenorrhea is classified as primary or secondary. The disorder is classified as primary amenorrhea if a healthy young woman has not started having menstrual periods after puberty, typically by 16 years of age. Secondary amenorrhea refers to periods that have been absent for longer than 3 months in a nonpregnant adult woman who previously had been menstruating.
If a young woman has not gone through any changes associated with puberty (such as pubic hair growth and breast development) and is not having any periods, she should be evaluated by age 13. Most young women begin menstruating by 14 years of age.
Menstrual cycle disturbances are one of the most common complaints causing women of reproductive age to seek medical care. An estimated 2% to 5% of women in the general population have amenorrhea. The prevalence is even higher in female athletes; an estimated 66% of these women do not get their periods.
Hormonal imbalances can inhibit normal menstruation. A part of the brain called the hypothalamus is responsible for producing a hormone called gonadotropin-releasing hormone (GnRH). Appropriate amounts of GnRH allow the reproductive system to operate normally. Stress, both physical and emotional, can inhibit the normal release of GnRH from the hypothalamus. This results in "hypothalamic amenorrhea", the most common cause of amenorrhea in women.
Thyroid malfunction—either hyperthyroidism, in which too much thyroid hormone is secreted, or hypothyroidism, in which thyroid hormone production is diminished—can also cause amenorrhea.
Imbalances of the hormone prolactin can also lead to amenorrhea. Prolactin is a pituitary hormone that is normally produced to allow for lactation after giving birth. In a woman who is not pregnant, however, prolactin elevations are abnormal. In most cases, prolactin overproduction is due to a small, benign growth (microadenoma) on the pituitary gland. Some medications can also elevate prolactin levels and cause amenorrhea.
Emotional and physical stress and eating disorders—including anorexia nervosa, bulimia, extreme dieting, and starvation—can upset the body's hormonal balance and cause menstrual periods to stop.
Excessive exercise and strenuous athletic activities also cause hormonal imbalances that result in amenorrhea.
Amenorrhea can be a side effect of other disorders. Very obese women sometimes do not menstruate because excess fat cells can interfere with ovulation.
Cushing's syndrome—a very rare disorder caused by increased secretion of a steroid hormone (cortisol)—is characterized by amenorrhea, as is polycystic ovary syndrome. Polycystic ovary syndrome is a very common disorder characterized by multiple ovarian cysts.
In some women, menopause occurs prematurely, before the age of 40. In these cases, premature ovarian failure is the cause of the amenorrhea.
Amenorrhea may be a side effect of certain drugs, including sedatives, hormones, oral and injectable contraceptives, barbiturates, and narcotics. Some women stop having menstrual periods for several months after they stop taking birth control pills.
Amenorrhea can be caused by various anatomic and genetic conditions Figure 01. While there is usually a small opening in an intact hymen (the membrane that covers the vaginal opening), some women have a hymen that contains no opening at all. In such cases, menstrual flow cannot pass out of the body.
Figure 01. Female reproductive anatomy
Some girls do not go through puberty, and do not begin having menstrual periods. In rare situations, a young woman may lack certain female organs (such as the vagina, uterus, or ovaries), or these organs may not be formed normally.
Disorders of the uterus such as Asherman's syndrome, which is characterized by adhesions or scarring within the endometrial cavity, can cause amenorrhea and infertility.
Women who have been injured, who have autoimmune disorders or pituitary tumors, or who have undergone chemotherapy, may experience ovarian failure that results in amenorrhea.
A genetic disorder may also be the cause of amenorrhea. For example, women with Turner's syndrome have one X chromosome instead of two. This abnormality prevents the woman from going through normal sexual maturation. Consequently, menstrual periods do not occur. Another genetic disorder, androgen insensitivity syndrome (also called testicular feminization), affects the development of the reproductive organs. In women with androgen insensitivity syndrome, the genitalia may look normal, but the internal organs are undeveloped. Because these women have no ovaries or uterus, they cannot menstruate or become pregnant.
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