I am not sure if this is still an issue, but i do have experience in this area...My last period was in december of 2010. The one before that had been in April 2010. I was most definitely not pregnant, as I had a tubal in '97.

The doctors can give you progesterone pills, like provera or prometrium, to induce bleeding, which they would recommend every three months if you were still missing periods.

It can become dangerous if you miss too many cycles as the lining of the uterus could continue to build up (since it is not being shed each month.) This thickening of the lining can put you at a higher risk of developing uterine cancer.

I do caution women however...if you are dealing with any mental health issues, for example, I am bipolar, these progesterone hormone pills can cause severe mood swings.
I personally can not take them because of this.

I hope maybe this info helps...
love to all,
Karma