Amenorrhea is when a woman of childbearing age fails to menstruate. A woman normally menstruates every 23 to 35 days.
The part of the brain called the hypothalamus regulates the menstrual cycle. The hypothalamus stimulates the pituitary gland. The pituitary gland lies just below the hypothalamus at the base of the brain.
The pituitary gland releases two hormones that regulate the female reproductive cycle. They are luteinizing hormone (LH) and follicle-stimulating hormone (FSH).
LH and FSH influence the production of estrogen and progesterone. These hormones control cyclic changes in the lining of the uterus. This includes menstruation.
In order for a woman to have regular menstrual cycles, her hypothalamus, pituitary gland, ovaries and uterus must be functioning properly. Her cervix and vagina must also have a normal anatomy.
There are two types of amenorrhea:
Primary amenorrhea occurs when a woman has not had her first menstrual period (menarche) by age 16. This condition is also called delayed menarche. It is most often due to late puberty.
This is fairly common in teenage girls who are very thin or very athletic. These young women are typically underweight. Their bodies have not experienced the normal puberty-related rise in body fat. This rise in body fat triggers the beginning of menstruation.
In other girls, the delay of menstruation may be caused by a genetic disorder. Or it may result from abnormal female reproductive organs.
Secondary amenorrhea occurs when a woman has experienced menstrual periods, but stops menstruating for three or more consecutive months.
Secondary amenorrhea can be caused by:
Pregnancy (the most common cause)
Menopause, the normal age-related end of menstruation
Emotional or physical stress
Rapid weight loss
Frequent strenuous exercise
Hormonal birth control methods, including birth control pills, the patch and long acting progesterone.
Polycystic ovary syndrome. This condition is associated with a tendency to be overweight, excessive body and facial hair and hormonal irregularities.
Premature ovarian failure (menopause before age 40)
Hysterectomy (surgical removal of the uterus)
Abnormal production of certain hormones, such as testosterone, thyroid and cortisone.
Tumors of the pituitary gland
Female athletes, especially young women, are more likely to have amenorrhea. Exercise itself does not cause amenorrhea. But it is more likely in women who exercise very intensely or who increase the intensity of their exercise rapidly.
Secondary amenorrhea occurs quite often in women who engage in activities associated with lower body weight, such as ballet and gymnastics.