I have good news and bad.
Me - I was an A prepregnancy. Went up to an E. Stayed a DD while Bfing. Stopped at 6 months. Now I'm a C. I am actually trying to relactate so who knows what they will end up like.
Friend - DD prepregnancy. G while Bfing. B now.
It really depends on your body. Also, don't freak out if they are no longer the same size. My left is smaller than my right. Just thought I'd throw that in there because I freaked when I noticed it.