smoking marijuana while pregnant?

So I'm not trying to start a debate because I honestly have always been against it, but now don't know how I feel about the issue. A good friend of mine is pregnant and she smokes marijuana pretty much every day. She's smoked for years, initially started for medical benifits, I was surprised she didn't stop when she got pregnant but she says it's really nothing to be concerned about. I was just curious about what other people thought about it, not that it matters, it's her body and her baby so I'm not going to tell her what to do. Just wandering what other folks opinions were on the matter.