I agree with this so much! There is another reason not to ask, as well. She might have just had a baby!!! Most women still look pregnant the first few (ok, in my case it was more like 6 weeks!) weeks after giving birth. I had someone congratulate me that I was "working on a sibling" for my baby when I was 6 weeks post partum. I was like, I'm not pregnant, this baby is 6 weeks old. It was awful. I went home and cried and didn't go out in public again for several days.
RE: Don't Ask Me If I'm Pregnant: Why You Should Let ME Tell YOU When I'm Ready