That kind of sudden weight gain certainly can happen with undiagnosed hypothyroidism. A well-known patient advocate, Mary Shomon, talks about gaining 30 lbs in the months before her wedding from her undiagnosed hypothyroidism (can you imagine how disheartening??? Dieting and still having to have your wedding dress let out?).
If your mother's diabetes is type I (insulin-dependent) then that does increase the risk slightly that your D might have thyroid disease.
Let's see what test was done on your D. Most likely they only checked a TSH. This is often done as a screening test, but can be inadequate sometimes for two reasons: - some people may have borderline normal TSH but still have symptoms of thyroid disease - in some of these cases, their TSH levels have not caught up to their falling thyroid levels yet. New guidelines for what is considered normal were approved a couple of years ago but still controversial, so sometimes the doctor or lab may be using the old standards.
- a second possibility which can be missed by just testing the TSH is secondary hypothyroidism, due not to failure of the thyroid gland, but failure of the pituitary to send the TSH message to the thyroid. These people, instead of having a typical hypothyroid picture of high tSH/low T4, will have normal (or low) TSH and low T4.
Ideally, they would check her TSH, free T4, and free T3, along with thyroid antibodies, but that is seldom done. You usually have to specifically request that they all be done. Total T4 levels can be falsely high in women taking birth control pills - I imagine the same error can occur with the shot, but don't know that for sure. Free T4 measures the actual amount of working thyroid hormone, instead of the amount bound to protein (which is the inactive storage form).
Weight gain is a side effect of Depo-Provera - if it is due to this, the gain should gradually stop as the hormones wear off, although she may have to work at diet and exercise to get back to her original weight.
Cushing's disease is another, rarer cause of unexplained weight gain - abnormally high cortisol levels due to adrenal or pituitary problems. Causes weight gain in a pattern similar to people who have to take steroids like prednisone for a long time - moon face, fatty back of the neck called a "buffalo hump", apple shape. This doesn't sound as much like your D.
Has she really gained 30 lbs. without ANY increased puffiness in her face? If so, then I might also wonder about a real longshot. I once knew a woman who had an extensive DVT (blood clot) in the veins of her pelvis while pregnant that affected both her legs. This would be really rare, though - most DVTs affect one leg or the other - I just throw it in because of your comments about how oddly distributed you thought her weight gain was. (Then again if she's naturally a "pear" like me - that's where we store our excess weight ).
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