If he is not putting his mouth on you & blowing forcefully, he's fine. Blowing air into your vagina can cause an embolism & that can be extremely dangerous. Just tell him you are a lollipop, not a balloon, & that should give him a good idea of what's safe.
Blowing air in the vagina regardless of being pregnant or not can be really dangerous but I'm pretty sure you have to like full on take a breath and exhale up there lol.