Licking is fine, but your partner shouldn't blow into your genital area. Forcing or blowing air into the vagina could cause an air embolism (a bubble of air that gets into your blood circulation). This happens very rarely, but it could be life-threatening for you or the baby.
There are a few things that are strange about this, namely, that there's a kinky, highly-enjoyable oral sex act that I've apparently been missing out on, considering that the inclusion of this information is pretty much universal in pregnancy sex literature. I've never heard of vaginal blow jobs. Neither have any of my girlfriends with whom I conferred on this topic. However, it must happen, as Cosmo has covered it.
According to one website, Go Ask Alice, the risk of danger for a woman is increased when their pelvic vessels are enlarged, which is what happens during pregnancy. And whomever is going down on you has to basically have a great set of lungs and try really hard to kill you by forcing "a very large amount of air" directly into the vagina, without allowing any to escape—meaning that s/he would have to cover the whole area with his/her mouth, creating a sort of vacuum seal.
But I couldn't find any instances in the news of a pregnant woman actually dying from oral sex. However, an entire article was devoted to the subject—that included five real-life cases—in a 1967 edition of Obstetrics & Gynecology called "Fatal Air Embolism in Pregnancy Resulting from an Unusual Sexual Act." All of the cases (which are fascinatingly salacious for the time period) involved pregnant teenage girls who died from air embolisms. Their partners all reluctantly admitted to having blown air into their vaginas.
Image via Amma Cat/Shutterstock