You do know that a lot of women are way more in the mood because of elevated hormone levels during pregnancy, right?
It's just the thought of uh, bumping into the baby, right, not the fact she's getting big? Don't worry about bumping into the baby, not an issue. Far more important is for her to feel secure, attractive and loved by you and you not wanting sex with her is not helping that. I assure you, as long as her pregnancy is healthy you can't affect the baby in any negative way, and she wouldn't let you hurt her or the baby so if your wife wants lovin' do your duty to the best of your ability, Woot, that's an order. If you're really concerned, pick a low impact, low penetration position (like spooning) but really you shouldn't need that until the final trimester. Nookie is good for all of you.