Just make sure you get fitted! So much better for your back and your breasts!
There is nothing worse that wearing a 14DD if you should be wearing a 10F
I completly agree dragoncookie.
Chody when you do go to get fitted for your maternity bras (if you haven't already) make sure it's from a proper bra fitter who measures you. I went into what I thought was a reputable bra merchant and the girl in there treated me like I was just fat. Even though your breasts are getting bigger if you put on a bra in the store and it doeasn't feel supportive it's going to feel worse when your feeling fuller.

Good Luck