I honestly don't think they'd write her being pregnant into the show. It just doesn't really mesh with things right now. Would she take a leave of absence from work? Would she still pull double or triple shifts with a baby at home? *shakes head* No, it just wouldn't work. If Anna really is pregnant, which I can't begin to guess about or comment on, I think they'll conceal it as much as possible on the show--have her in the lab a lot, find clever ways to hide her stomach, etc.
But I really think we're all giving this way too much thought considering that it's all speculation and guessing at this point.