Unless you enjoy being slapped
Things never to say to a pregnant woman:
1. "Hey there, big mama!"
2. "My gosh, you're enormous! Are you sure you're not having twins?"
3. "Well, looks like the boob fairy has visited you!"
4. "Should you really be eating that?"
5. "You shouldn't be feeling so cranky/tired/uncomfortable. You're not THAT pregnant yet."
6. "Are you still with the father?"
7. "Is this your last? Are you getting spayed after this?"
8. "Wow, that really is an outie!"
9. (Males only) "Yeah, the pregnancy has been hard on me, too."
10. "Pregnant women are so beautiful." (They'll never believe you.)
Better yet, just avoid speaking to pregnant women.