I had the opposite experience with my first baby - people seemed genuinely surprised that I was pregnant right through the second trimester. I actually bought a t-shirt for the gym that said "Yes, I'm pregnant."    I was measuring normally and all that, nothing weird about the uterus... I eventually figured out that having wide hips and being surrounded by landwhales, my belly just didn't look out of place. Most of the female population looked five months gone, so people stopped assuming that protruding stomach = baby on board.