Okay, I may get flamed for this one, but...
One person already mentioned that years ago it was more than acceptable to smoke while pregnant and had extremely healthy babies that grew up to be very healthy adults, etc. That said, there is a great deal of evidence that there is a greater risk to the baby if mom-to-be does smoke. It's everywhere you go -- smoking is BAD, not allowed anywhere!
I smoked through both pregnancies...I cut down a great deal from what I had been (one pack to 1/4-1/2 per day). I have one boy that rarely shows symptoms that are asthma-like and one that is healthy as a horse. Odd thing is that I smoked more with the latter. Go figure.
I had asked my doctor about it at the time and was told that it would have been best if I had quit before getting pregnant, but that a cold-turkey approach could stress the baby. I was also told that a mom's stress is very harmful to the baby...oftentimes more so than a cigarette or two. (Kinda' like a glass of wine is ok, but getting drunk is definitely not.)
I think telling her to ask her doctor about it and that you're concerned about it is the extent of where your responsibilities lie. If you badger her about it, you will cause her stress (bad for baby), probably make her smoke more because of the added stress or out of defiance (bad for baby), and eventually damage your relationship (bad for everyone). Bottom line is, it's her baby, it's her body, and it's her decision. You can support her without supporting her choices.
I know I wouldn't like someone on me every day telling me not to eat such-and-such because of this-or-that, raise my children this way because so-and-so says to, etc. I don't mind caring advice, but don't judge me if I don't agree or do what you suggest. Just because it's different, doesn't make it wrong, and who's to say who is right???
(Just an fyi, I don't smoke in the house or car and keep the smoke away from them as much as possible at all times. I don't change my shirt and I have my coat in the house. On another note, given all the chemicals most people use to clean and cook and drive, those fumes are probably just as bad for us. How do you keep all the other airborne toxins away from your children? What about the fabric softener used in the dryer, detergent used that doesn't get completely rinsed out, cleaning solution that got on your clothes? Sometimes, I wonder if some people aren't getting to the point of having to rinse off in a stream and only hold their babies when naked!)
Sorry for the rant, everyone, but sometimes people go off the deep end on what's politically correct, etc, and forget that we live in "the land of the free" which means living by our own choices and laws...not someone else's. I guess what I'm saying is, Live YOUR life...not someone else's.