It is in your best interests to never, ever ask a woman if she is pregnant. On the one hand, yes, if you're right, she will likely coo and tell you all about it. However, if you're wrong, you now have either a very pissed off woman wanting to know why you think she's pregnant. Are you saying she's fat? or you have a very awkward conversation to extract yourself from. It's fun to watch from the outside of the conversation, but I'm guessing not so much from the inside.
No, this did not happen to me. It was our Editor asking one of the reporters. She's a tiny little thing and she wore a baby doll shirt, which do tend to make women look like they have a little bit of a baby belly going on. He's lucky she has a great sense of humor and is very easy going. But it was a very amusingly awkward conversation to watch him try and get out of.