This should perhaps be in maternity wear. Currently abroad, where the maternity wear is pants, DH is back in the UK and I was going to have him bring me back a couple of dresses for formal stuff. I have this in a size 2 but I'm a little busty for it, I was going to get a size 3 in other dresses but they've changed the sizing do you follow bra size which would make me a dress size 14-16 or pre pregnancy dress size 12-14 which doesn't cover my cup size 34 F/G. I'll be wearing dresses in about 2 weeks when I'll be c. 35 weeks.
I had one a couple of years ago and really had to size up. My normal size is a 8/10 and I think I ended up with the size equivalent to a 14/16. It was a jersey dress though so maybe a little less forgiving on the bump than some other styles.