Ranting: first rude comment!

So I've tried not to let it bother me but it kinda does. 
Yesterday I saw a friend from my work and she was telling me that someone else at my work said that she thinks my pregnancy is bullshit because before I was off I wasn't showing. When I left work 3 weeks ago, I was just over 19 weeks. I was wearing maternity pants (we wear a uniform), my shirt was tighter than it had been before before getting pregnant and I'm a bigger girl to begin with, so I never expected anyone to really notice whether I was showing or not. I don't understand why people think it's okay to talk about others behind their backs to someone's friend... Did she honestly think that I wasn't going to find out? I would never say anything about this girl behind her back. Thank goodness for friends and being there for me because when she heard that she told the girl not to open up a can of worms before not knowing the facts.