If you really want to have a nursing bra immediately buy the cheapest one you can find. There really is no way to guess your size. Pre-pregnancy I was a 34 B, at the end of my pregnancy I was a 38 DD. When my milk came in around day 4 I didn't really get bigger, my boobs were just incredibly full and hard like I had brand new implants. At 3 weeks pp I'm down to a 36 C and still successfully bf'ing.                
                             
        
Re: from 0-3 - nursing bra advice
i would wait until ater the baby to buy one no way of knowimg how big you'll be.
Emily 8.8.08
Madeline 1.2.11
William 8.5.12