The back keyhole needs covering floral dress. My client did not want her bra to show on this dress. Maternity bras tend to be quite wide at the back and this was the issue for her. It would have been a nice feature with the keyhole, but it really didn't work. The bra was fully exposed from one side to the other.
I created a shape to insert behind the opening. I used two layers of fabric, because I wanted it to be reasonably thick. Otherwise it would have folded when it was on. I thought about using an interfacing, but decided against it.