We're almost 12 weeks along and man, have I learned a LOT! Maybe I'm a little sensitive, but I propose the following rule of thumb:
If you wouldn't say it to a non-pregnant woman, don't say it to a pregnant woman.
This includes all comments referring to "getting big," and all personal questions (e.g., are you constipated? can I see your tummy? how much weight have you gained?). While I am certain many of these comments and questions are simply a way to relate to the pregnancy and perhaps share your own experiences, we are still women, we may not want to share all of our business and our feelings do get hurt (hormonal or not, no woman in her right mind wants to be told how much bigger she's looking).

It is especially difficult as we read information about what is and isn't "normal." For example, I just read a newsletter that said at 12 weeks you "shouldn't" be in maternity clothes yet, and I've been in them since about week 7 (they're just so much more comfortable than my regular pants!). That said, I've only gained a couple of pounds, but when I wear the A-line shirts and dresses, I look very pregnant. Between reading about the "norm" and hearing the "getting big" comments, a girl's head is liable to explode, and that doesn't even factor in the hormonal surges.

So, on behalf of all the pregnant women out there, focus on the positive comments about how glowing she looks or what a good mommy you know she's going to be. Also, don't scare her with horror stories about your hairdresser's friend's terrible delivery. Again, I understand this may be just another way to relate to the pregnancy, but with all the bad news in the world, surround this little miracle of life with positive thoughts and energy. I guarantee every pregnant woman you ever run into will appreciate it!