I've had two wedding dresses that I've transformed into maternity gowns.. but that takes some imagination and a little bit of sewing skills ;)
This first one is from a vintage wedding dress from the '70's or '80's I'm assuming. I re-designed the neckline and shortened the sleeves. I also put in a corset style lace up back so I could adjust it to different sized models. (Even though I made it adjustable, it still only fits up to a size 8 because the dress was so tiny in the first place)