Jen, thats a hard one.
I havent been in that situation, so its difficult.
I think i would be tempted to find out, but then i would be concerned that if i did find out, and it was a boy, then perhaps (nasty thought) just perhaps i might not take as much care of myself as i should, KWIM?
If you dont find out, and wait till the birth, then do you think that you will have abit of PND, or probs bonding with the baby, if it is a boy? Maybe you could pre-empt the situation by thinking positive thoughts now in preparation for it.
But, whatever you decide, let us know, and i am sure that, if it is a boy, there will be lots of peoples that have been thru the same thing, and can support you thru this.
Hugs