depending on the size of your own body and the size of your baby you couls start to show around 4 months or even later...i know a girl that is nearing 6 months and doesn't really look pregnant......i also have a friend who didn't really look pregnant until she was around 7 or 8 months.....it all just depends on your own body.......
I didn't actually get noticably bigger until about 5 months. Then I grew like crazy, lol. at around 4 1/2 months i wasn't able to fit into my normal pants though. I think it all depends on your body type