Thing is - when your milk comes in, your boobs go huuuuuge and rock hard and it settles within a week or so.
So I think buying a bra when milk is in is poor advice. I did that last time and ended up with bras waaaay too big.
I going to get mine about 38/39 weeks.
I quite like the bra tops though. Nice and loose on sore boobs and you can just yank them up to feed :)
Peace - I think the tape measure thing also depends if you are lying flat or slightly up. A good MW will do it the same way each time