Terrace dress for maternity

Hi! I'm sewing the terrace dress for the first time. I'm making it for myself to match my daughter's dress (made from the building block dress book, so fun), and I just found out I'm expecting my 4th baby (hurray!). I'd like the dress to fit me through the summer, so say until about 7 months. For those of you who have sewn it before, is it *really* roomy in the front without the belt/sash, or should I maybe go up a size? (I figure it will work well to just make the veiw B thin sash/belt and put it up increasingly higher as my belly grows.) Thoughts?