I am 21+3, and my bump is, well shall we say "significant", struggling to get shoes on unaided already, etc, and it is very definately a baby rather than too many pies.
Having just moved house I went to the new GP to register, had an appointment with a practice nurse. She checked my name, DOB, took a wee sample from me, did my blood pressure, then said "And are you currently on your period?"
I was gobsmacked! Looked down at the huge mound of my belly and said "Er, well, no, I'm 21 weeks pregnant. ..". She did a double take,stared at my belly for a minute and, looking genuinely shocked and slightly horrified, said "Oh sorry, I hadn't noticed!"
I am still laughing about it a whole day later :)