I've read that it's best to be fitted for nursing bras...but in that case, should you wait until your milk comes in? Seems like you'd need them before then, but I'm assuming my boobs will be much bigger at that time!
The gal that sized me recently told me it would be a good idea to get a few soft cup ones until my milk comes in so they have a little give and then get some molded cup ones (if thats what you want) a little more true to size once the baby actually comes...
I went to JCPenney's and the bra consultant said anytime after 36 weeks is ok to get measured. Depending on the bra, the cup size is flexible enough to increase in cup size when your milk comes in.
I bought a couple soft sports nursing bras when I was very late in my pregnancy. I needed something comfy. Unless, they're returnable, I would recommend waiting as you don't know if you will be breastfeeding...baby may not latch, no supply, etc.
Re: when to buy nursing bras?
Good question, been wondering myself.