My boobs went from a B or C depending on the make to a C or D. DH's really charming way of putting it was "you used to have little princess tits but now you've got big mama boobs" #-o :-s
Tulip, a lot of women find that while they are pregnant the most comfy options are sports bras or maternity bras. There is an article about Maternity Bra's and Pregnancy on the Belly Belly main site that you might find useful.