By around the 12 wk mark the uterus is starting to grow above the pelvis and will be slightly starting to push out. By 20 wks the top of the uterus is about level with your belly button. I have seen women who show straight away and others don't look pg at 5 months. With my first pg I started showing by around 14 wks, but with the next two I was in maternity gear by 10wks.