I have learned that floral print dresses, especially those with a vivid background color, look wonderful on pregnant women. Here is another example of a dress that really works for the shot; its dark blue background and light blue and pink flowers pop wonderfully against the background of the trees and grasses of the park.
Another reason why this is one of my favorites is that it is a maternity portrait and also a family portrait. With everyone in blue, the color story is told against the natural background. Because Mom and Dad's faces can't be seen, the focus is on the little guy in the middle, adorable in his blue shirt, blue jeans and gray shoes. Without looking matchy matchy, this family looks stylistically cohesive and absolutely adorable.
Have you thought about combining a maternity portrait session with a family portrait session? You can see here that the result can be lovely and captivating.