Ha, just realised I can't answer my own question becasue I am a non smoker anyway and have never, yes never, actually seen a pregnant woman smoking and none of my friends smoked ( or drank hugely) in front of me while pregnant - what a sheltered life I lead
However, I did have an unsettling conversation with a pregnant woman I had a passing acquaintance with. I was in my local at the time, surrounded by people I knew. The woman struck up a conversation with me. She was about 5 months pregnant. I asked her how she felt etc etc as you do, and she told me how she'd only realised she was pregnant about a month before. She said how much drink, cigarettes and the odd illegal susbstance she had got through witout realising she was pregnant all that time. She was drinking something vaguely alcoholic at the time, but I didn't know if it was her first glass or her fourth. She told me her doctor said that since her baby was healthy and had survied those months so far, not to worry so much now, but just cut down if she could. I nodded away, feeling a bit uneasy, but since she wasn't actually doing anything apart from having a single drink I felt there was nothing I could say. I had drunk alcohol from time to time in the second trimester myself.
It was only later that my dh and a few other people who knew her better told me that had announced that she was pregnant ages ago and had disregarded advice to reduce her intake.
If this was so, she was in deep denial about this when she spoke to me. She had constructed an alternative story and seemed, I think, half way to believing it herself. She definitely didn't want criticism from me, but very obviously wanted spend and hour or so chatting about her pregnancy to someone.
Even when I knew this, I had no thought of going up to tackle her. Perhaps I should have, but if someone lies so convincingly, how do you know what is gong on underneath?