Pretty much everyone I know who uses cannabis vaporizes these days, so no burning involved. That said these sketchy vape cartridges are pretty scary at times and I'd love to see that regulated and tested like tobacco products are.

Regardless of how it's ingested though I imagine that once it gets into the bloodstream it's getting into the fetus, and I'd absolutely want a bunch of high quality peer reviewed studies saying that it's safe before I'd be willing to indulge while pregnant (not that it's an option for me, testicles and all).