"So, you're what, seven months pregnant now?"
"Uh, no, I'm about 21 weeks..."
"Wow, you've got a big one coming, huh?"
Well, sure, I guess so, hey, thanks for calling me fatso, I greatly appreciate it.
Actual (allegedly humorous) comment from previous pregnancy:
"Wow, you'd better stop eating in the cafeteria. You're starting to get fat!"
Why oh why do people feel the need to remark on your size? Seriously, no pregnant woman on the planet is going to hear that and *not* think "OMG I'm huge and ugly looking and I'm hiding in my bathroom until my water breaks." I get that it's a clumsy way of expressing interest, but either come up with something less clumsy or hey, say nothing. I do not have a giant neon sign on my belly saying "Ask me about my pregnancy." Sure, I'm thrilled about it, and I'm looking forward to holding my baby, but I do have, you know, stuff to do. There's an incredibly good chance you're catching me at a moment when I am not at all thinking about being pregnant and you might as well say "So how about those Yankees?" (For the record: Shame the winning streak ended, I think Teixeira and Swisher were good additions and the food at the new stadium is a huge improvement.)
As a rule, I don't make fat jokes. I've known too many people who struggled with weight issues to think that's OK. My two exceptions are professional athletes -- I don't care if you are a pitcher in a DH league, can't you at least try to look like you play sports for a living? -- and the late, lamented 20-pound cat who once belonged to my in-laws, informally known to everyone as Big Fat Kitty. Because seriously, he was a big fat kitty.
I especially dislike weight jokes made about women, since women are invariably, unfairly judged on their appearance and the threshold for what people seem to consider "fat" on a woman is unrealistic to the point of laughability. But to comment on the weight of a pregnant woman, who is gaining weight for a very specific reason and will have very little control over her appearance until well after the baby is born, just seems like a low blow no matter how it was meant.
What to say to a pregnant woman: "Congratulations. You look great!" The end.