I'm in my first trimester with a very high risk pregnancy. I asked my maternal-fetal medicine specialist about vaping. She asked what was in the liquid & when I told her propylene glycol (sp?), vegetable glycerin & flavorings, she said as long as there's no nicotine, she's fine with it.
Smoking aside, nicotine is a known vasoconstrictor. Without even going into what effects it could cause for the baby directly, nicotine causes the mother's blood vessels to constrict (much like caffeine, more or less) and that means cutting off at least some of the oxygen/nutrients that would otherwise be going to the baby via the placenta, which can cause a myriad of problems.
I also have to say that just because a lot of people smoke while they're pregnant & their babies turn out fine does NOT mean that it's ok. Lots of extremely risky pregnancies result in healthy babies while lots of perfectly "healthy" pregnancies result in less than perfect babies, even losses. The best advice is to eliminate as many risks as possible to increase the chances of a healthy baby. There are no guarantees.