Tell them you find their comments hurtful and inappropriate and ask them if they'd like you to comment on their bodies constantly. Seriously - you go to work to do a job, not make personal comments about people. If you've been discussing details of your pg with them, stop. I found this the most helpful strategy to shut down unwanted discussion with work colleagues. I just didn't discuss it with them in the first place. To me it was a personal issue and not something I wanted to broadcast at work. It depends on your work environment but I never brought it up. It didn't stop the questions and stupid huge/massive//big/twins comments but I always gave minimal and vague answers and most people got the hint after a while.

hun. A big baby is a good thing believe me, once it's born, you'll be wanting it to put on heaps of weight. (Not saying you'll have a big baby, just that if you do, there's an upside).