Here's an interesting article on uterine fibroids and their role in recurrent miscarriages.
I was diagnosed with 8 uterine fibroids (1 was the size of a grapefruit!). When we had completed 5 IUIs, all unsuccessfully, we prepared ourselves for IVF. It was explained to us that the fibroids themselves weren't dangerous, but they might get in the way once we began IVF treatments. Our chances, from a statistical standpoint, would have gone from about 45% to 20%, if I did not have the fibroids removed.