I always find it best to try on. I got measured in mothercare for maternity bras and my one was great. I've bought a couple of nursing bras from debenhams that I tried on, didn't get measured for these but they are grand for now. Like podpie said, they fit on biggest back, have extenders in case I get bigger and can tighten as back (hopefully) goes down.
Well reflexologist hasn't kick started labour but she did manage to activate my bowels and my milk has stepped up too, all I have to do is touch my boob and it comes out! Had a couple of periody pains last night but not strong or regular. Let's see what hospital appointment today brings, I really don't fancy the induction process.