I saw the first photo yesterday and wanted to comment, but I couldn't put the right words together for what I was feeling about the (first) shot.
Now seeing the other shots, it's more clear.
I think the first one felt a bit off because of the way she was looking right at the camera. That is, of course, usually what you want in a portrait, but it felt weird in a maternity shot. I think it's much more common for the woman to be looking at her belly, or at the father. Common doesn't mean better, but I think that maybe it's just more effective that way. By looking down at the belly, it draws the viewer's attention to it, including it as one of the subjects of the photo. Otherwise, it's just a portrait of a woman who happens to be pregnant, if you know what I mean.
It's still a good shot, I can't find any fault, but the 2nd one 'feels' like it captures the mood better.
I'm surprised you haven't done much maternity. You should do more, these are great.