• The ovaries are not being told what to do. Excess exercise, low body weight, and eating disorders all adversely affect the pituitary gland, so that it doesn't send proper signals to the ovary. Girls with these conditions are found to have very low levels of estrogen; they do not bleed in response to the progestin challenge and do not release eggs. (This physiological response more than likely evolved in times of great stress or starvation, when it was better not to get pregnant.)
  
  If a girl develops an eating disorder or follows an intense exercise regimen before puberty begins, it can result in a total delay of puberty (affecting breast development, height, etc.).
  
  If these scenarios develop after puberty has already started, a girl may have some breast development already, but menarche will fail to follow. If a girl who has already started getting periods then develops an eating disorder or takes up a strenuous exercise regimen, her periods may stop--a problem all too commonly seen in competitive gymnasts and dancers.
  
  It's important to note that eating disorders often are not diagnosed until a subsequent medical problem develops--absent menstruation being one common such problem. Of course, not all girls with eating disorders exercise, and many girls who exercise don't have full-blown eating disorders. But both of these conditions, either alone or in combination with other stressors, can lead to lack of periods. When a teenage girl's periods do stop, it offers her doctor an opportunity to not simply evaluate her hormonal status, but to also ask important questions about her body image, feelings of self-worth, and attitudes toward food.
  
  Some girls have this low-estrogen hormonal situation despite the absence of the above specific causes. Administering a CT (computerized tomography) or MRI (magnetic resonance imaging) scan of the brain can rule out the possibility that a benign tumor of the pituitary gland is responsible for the lack of periods.



• The ovaries are unable to make hormones. If a girl (or woman) is diagnosed as having a low-estrogen state, the next step is to test the blood level of the pituitary hormone FSH. This hormone, produced by the pituitary gland, serves to tell the ovary to make estrogen and to ready the eggs for ovulation.
  
  If the ovary doesn't have any eggs, or if it can't release them, the pituitary sends out more and more FSH in an attempt to get the ovary to respond. For the girl who is found to have a very high FSH level, it's a sign that the pituitary is, in essence, screaming at the ovary to get going and that the ovary isn't responding.
  
  Delay of puberty, delay of menarche, or loss of periods characterized by low estrogen levels and an elevated FSH level is an indication that something is wrong with the ovaries. Releasing eggs and making hormones go hand in hand, so if eggs are not present, estrogen won't be produced. Genetic conditions like Turner Syndrome, which also may be associated with short stature, can lead to ovaries that don't make eggs.
  
  Girls who have had radiation therapy or chemotherapy for cancer find sometimes that their ovaries don't work properly afterward. This depends on the type of chemo involved and whether the ovaries were in the field of radiation. Ovarian problems represent serious conditions that need to be explained in more detail by the physician.

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