In some cases, the reason is clear: you've had your ovaries surgically removed, have a family history of early menopause, or had ovarian damage due to cancer treatments.  But sometimes the causes are less apparent and can leave you wondering: How did this happen to me? Here, then, are the common causes of the various conditions that we often refer to as early menopause:

CAUSES OF PREMATURE OVARIAN FAILURE (also known as Premature Menopause)  (For more information about POF, see POF Fact Sheet.)

• Autoimmune Disorder
  This is a common cause of premature ovarian failure. In fact, some recent studies have shown that up to two-thirds of the women with premature ovarian failure have it due to an autoimmune disorder. When this happens, your body's immune system mistakenly attacks itself. In effect, your body senses part of itself as an invader -- so it sends out antibodies to destroy this perceived threat. In the case of premature menopause, you may have antibodies to your own ovarian tissue, to your endometrium,  or to one or more of the hormones regulating ovulation.  These antibodies attack your reproductive system, and may interfere with and ultimately destroy your ovarian function.  If you have a family history of autoimmune disorders or have one yourself (such as thyroid disease, diabetes, or rheumatoid arthritis), this may be the cause for your early menopause.

• Chromosomal Irregularity
  Some cases of hereditary premature menopause are caused by defects on an X chromosome.  It's a very complicated topic, but, briefly, here's what happens:   Women have two X chromosomes -- and, even though only one of these chromosomes is active, a defect on either one can cause premature menopause.  This defect, sometimes called "fragile X syndrome," apparently interferes with the production of eggs.   So if you are a fragile X carrier, you have a lesser number of eggs in your ovaries, which in turn leads to an earlier menopause -- generally at least six to eight years before other women. Another related form of genetically-caused premature menopause is called "Turner's Syndrome."   In this case, you're born without a second X chromosome -- or without part of the chromosome.  Since you need two X's for your ovaries to develop properly, a missing X or a faulty X leads to deficient ovarian development (called ovarian dysgenesis).  Often women with Turner's Syndrome never have their periods at all, since their ovaries never develop enough and don't produce ovarian estrogen.  On the flip side, some women enter premature menopause because they have three X chromosomes --  which interferes with ovarian development as well.

CAUSES OF EARLY MENOPAUSE DUE TO SURGERY

• Oophorectomy and Total Hysterectomy
  This is one of the most common causes of early menopause -- and often one of the most difficult to deal with, since you are coping with the fallout from surgery as well as sudden menopause. In this case, you experience premature menopause after  removal of both of the ovaries (a bilateral oophorectomy) or removal of the uterus, both fallopian tubes, and both ovaries (a total hysterectomy).  Because both of your ovaries are removed, your estrogen and progesterone levels plunge, leading immediately to menopause.  You may experience more intense symptoms than those who go into premature menopause spontaneously because of this sudden drop.

• Ovarian Damage Due to Other Surgical Procedures
  Usually, as long as you have at least one ovary, you can continue producing hormones and shouldn't go into premature menopause.  But in some cases after a hysterectomy in which one or both ovaries are left intact, one or both of them fail --- either immediately after surgery or up to a few years later.  This may happen when the ovary or ovaries are damaged or otherwise affected by such procedures as cyst removal or when the surgery damages blood vessels and so interferes with blood flow to the ovaries.  In this case, the follicles on the remaining ovary/ovaries  slowly die out, resulting in menopause.  Similarly, some women experience premature menopause after tubal ligation (getting your "tubes tied" as it's commonly called). Again, this is a result of the surgery interfering with blood flow to the ovaries -- which ends up causing eventual ovarian failure.

CAUSES OF CHEMICAL EARLY MENOPAUSE:

• Radiation Therapy and/or Chemotherapy
  With the rise in cancer treatments has come a rise in premature menopause due to these treatments.  Unfortunately, the significant doses of  radiation or chemotherapy used to kill cancer can also damage the ovaries -- resulting in premature menopause.  In some cases -- especially when you've received low dose/short term treatment, you may experience temporary menopause due to chemo or radiation therapy.  Your ovarian function may stop working regularly for a few months after treatment, but then return to normal after four months or so.  But often, even when your periods return, you remain infertile.

• Tamoxifen
  Tamoxifen used to be prescribed after you were diagnosed for breast cancer -- and, as with other forms of chemo, you would run a risk for premature menopause as a side effect. But recently doctors have begun prescribing Tamoxifen as a preventative to women with a high risk for breast cancer, since it cuts breast cancer rates by about 45 percent.  While the media has focused on the positive aspects of this drug (and there are many), there is an important potential side effect to Tamoxifen that hasn't been played up a great deal: it can send you into premature menopause.  This happens because Tamoxifen takes the place that estrogen would and so acts as an estrogen-blocker.  Since your body isn't getting the regular amount of estrogen it would naturally get -- and since low estrogen levels signal your body to produce more FSH -- your body ultimately may react by entering menopause prematurely.  One important point:  Often this is a temporary effect and regular ovarian function returns.

OTHER CAUSES:

• Family History
  It's not a hard-and-fast rule, but most women go through menopause at about the same age their mothers did -- which means that if there is a family history of premature menopause (your mother, your grandmother, your sister), there's a chance that you too will experience it.  Some studies, however, seem to indicate that only about 5% of all women who are prematurely menopausal have a family history of this condition.  So family history is not necessarily destiny, but could be an early indicator if you suspect premature menopause.

• Viral Infections
  If your mother contracts a viral infection while you're still in her uterus, it can affect your ovarian development, causing you to be born with lower number of eggs than you otherwise would have had.  In this case, since you start with fewer eggs than most women, you run out of eggs more quickly, which results in premature menopause.   Similarly, some studies theorize that a small number of women may experience premature menopause if they have had mumps and the infection spread to their ovaries.

OTHER DISORDERS THAT MAY CAUSE MENOPAUSAL SYMPTOMS
It's important to realize that you may have menopausal symptoms, but not be going through menopause or ovarian failure.  Other disorders --  many of which are treatable -- can cause symptoms that overlap with those of menopause.  This is one of the reasons it's very important to speak with your doctor and be tested to determine what is the cause of your symptoms.  Among the other disorders that can cause symptoms similar to those of menopause are:

• Thyroid Disease:  Both hypothyroid and hyperthyroid often cause symptoms that mimc those you get when your hormone levels drop.   This is particularly true of hypothryoid -- which can cause hair loss, weight gain, moodiness (the "blahs"), and amenorrhea -- the stopping of your periods.    Hyperthryoid can cause palpitations and sweats (that may seem like either hot flashes or night sweats).  In both cases, though, proper diagnosis and treatment will result in the reversal of symptoms.  (One important note:  As mentioned before, often women with premature ovarian failure have a tendency towards autoimmune disorders such as thyroid disease -- so you may have both POF and thyroid disease.)

• Hyperprolactinemia:  This is a disease that is marked by overproduction of prolactin -- the hormone that is reponsible for milk production in your breasts.  Often women with hyperprolactinemia also go through amennorhea -- the stopping of their periods.  Unlike premature ovarian failure or early menopause, however, hyperprolactinemia isn't caused by ovarian failure and low production of estrogen.  One of the typical signs of hyperprolactinemia is galactorrhea -- which is the technical name for milky discharge from the breasts.  To determine if this is the cause of stopped periods, typically a doctor will need to check your prolactin levels.  Hyperprolactinemia is often treated with different drugs, such as Parlodel, which typically results in the return of normal ovarian function.

• Pituitary and/or Hypothamic Disorders:  Often women with pitiuitary disorders (such as hypothamlic or pituitary failure or pituitary tumors) go through amennorhea.  In this case, typically they do NOT have the typical symptoms that arise with low estrogen (hot flashes, etc.), but do find that their periods have stopped.  Usually, in this case, you will have normal or even low LH and FSH levels, but may have elevated prolactin levels.  You may need to get a scan to determine whether you have a tumor or lesion, which is typically treated through surgery or medication.
  
• Cushing's Disease:  This occurs when your adrenal glands are overactive -- resulting in amenorrhea.

• Polycystic Ovarian Syndrome (PCOS):   Also known as polycystic ovarian disease (PCOD), this can cause skipped periods and a number of other symptoms, including excessive hair growth..  This disorder is sometimes diagnosed by checking your hormones -- as a high ratio of LH (luteinizing hormone) to FSH (follicle stimulating hormone) is often present.  This disorder is also sometimes marked by a high level of androgens -- testosterone and DHEA.

• Other causes of amennorhea (stopped periods) include:  Excessive weight gain or weight loss; use of certain drugs (such as phenothiazines -- which are psychiatric drugs, and certain narcotics); excessive exercise;  recent use of birtch control pills (it's not uncommon to stop getting periods for up to six months after discontinuing the pill.  However, if your periods don't return after this time, this may not be related to the pill); uterine adhesions (usually due to infection or d&c procedures).

In the above cases, usually your doctor will be able to determine the cause of your symptoms through blood tests or giving you a "progesterone challenge" test -- which can help determine why your periods have stopped.