Smoking weed while pregnant?

I thought this would be a good topic. I've always said I'd rather see my friends and family smoke bud then do herion or any other really bad harsh drugs. Anyway I've never questioned smoking bud while pregnant. I didn't know people did that. Recently a friend of mine found out she was pregnant I went to her house and she was smoking. I asked her what she's doing and reminded her of the fact that she's pregnant. She said it's OK, my midwife told me she rather see her mom's to be smoke bud then a cigarette. And that there is no scientific proof that bud causes any birth defects or harms the fetus in any way. What is everyone else's take on this. is my friend lying to me? Is it safe to smoke while pregnant? If you have any proof of things could you please leave it in the comments. I honestly can't wait to read all of your responses and possibly send them to my friend