Someone I was friends with back in high school had no idea she was pregnant.  Normal size woman, about 29 or 30 years old. Had a child the year before. Had horrible pain and went to the ER. Turns out she was six months pregnant.  She ended up having tyroid cancer which somehow prevented her from gaining weight. That part I heard from a friend though. She had the baby at eight months, went through some sort of treatment for the cancer and is completely fine now. The baby was very small and in the hospital several months but as far as I know the baby is healthy and developing normally six years later. I think her situation was just a fluke though.