Based on their sizing chart which goes by your pre-pregnancy size, I ordered a medium which turned out to be way too small.  I'm only halfway through pregnancy and getting nursing bras now for comfort and to test them out before I really need them.  I may have gained a little more weight that I'm supposed to at this point, but even without that it's hard to imagine this would have fit at 9 months or after birth when your breasts grow even more.  So you might want to go a size larger than they recommend.

Instead of returning for a bigger size, I've decided to go to one of their stores to look for another model because the design of this doesn't allow you to expose just one breast.  To get one out, you'd have to unclip and take down both sides, and at that point I might as well just be wearing a regular bra and undo it altogether.  And now that I think about it, I'm not so sure about the concept of a sports nursing bra anyway; am I really going to work out and then offer my baby a sweaty breast?