I don't think that actually having oral sex is unsafe. I do know that air should not be blown into the vagina...Which can be part of the fun in oral sex. Blowing air into the vagina can cause a lot of problems. I would contact your ob just to make sure. But I am pretty positive that regular oral sex is fine as long as he/she doesn't blow air into the vagina.
Hope this helps.

I heard exactly what ct just said :)

Oral sex is fine. Blowing into the vagina during oral sex is a big no-no. Blowing can cause air bubbles in the bloodstream and can be very harmful.I wouldn't give up on oral sex just be careful.

this is exactly what I heard a few years back. But I have also heard it can give infection to the baby.