First of all, congratulations!
Second of all, I don't think you'll find anyone who would claim that the tumor itself is harmful to a pregnancy. Personally, I went through two pregnancies with the tumor in my head (I was diagnosed right after my second child was born), and have two healthy, happy boys.
These tumors are so slow growing that even waiting another 9 months (given that you've already had surgery to remove most, if not all, of the AN) should not pose a risk. The big question is whether or not to have an MRI while pregnant. The MRI itself poses no risk, in my understanding - it's the contrast agent (usually gadolinium) that's questionable. And an MRI for an AN is useless without the contrast. If you google "pregnancy" and "gadolinium" you'll find lots of articles. It looks like MRIs with contrast during pregnancy are accepted in Europe, but the FDA hasn't approved it in the States. Personally, I never had an MRI while pregnant (again, I wasn't diagnosed until after) but I did while breastfeeding after my son's pediatrician looked up the drug interactions for me and said it was okay.
What would I do? Talk to the OB about the safety of an MRI with contrast, and talk with your surgeon about delaying the next MRI and what that could mean. And walk carefully - that big old belly at the end can throw anyone off kilter, let alone someone missing a vestibular nerve!
Best of luck to you and your family! As others have said, there are lots of stories here about AN patients and their healthy babies. Finding some of them may help reassure you. And soon you'll be able to add your story to theirs!
Katie