Totally contradicting what i said before, totally agree with above, forgot that if you have had pervious children you can show earlier. I have a bump already but it's not a baby bump, it's more of a bloated bump. Despite this, I'm still proud of it!! My trousers are all too tight and cause pain if I sit down in them done up, yet the baby is still probably too small to be a real baby bump.
Who know's , I guess once you cant sit down in your trousers with them done up - or stand up with them done up, then that's your bump!