Unrequested C&C, feel free to ignore this.
One thing to keep in mind during a maternity shoot is that shooting straight on to the mom-to-be is rarely the most flattering angle - this is true even of non-pregnant female subjects. That's not to say there aren't exceptions, because there are even in this set, but among other things shooting straight on to the belly really minimizes the curve of the baby bump compared to a profile or 3/4 angle perspective. Of the six shots in this set, five are straight on, and IMHO it only works in one of those. Now, for some individual C&C...
Shot 1) The perspective here really shows off the baby bump, and the pose (looking down at the belly, arms "supporting" it) is a classic, tender maternity pose. The background is busier than you usually see in this kind of shot but I don't think it distracts from the subject and gives the shot overall some more interest than if everything had been flat, solid blocks of color. A dark shirt may have helped define the belly a bit better, but it may not have.
Shot 2) A cute shot of the couple but it doesn't do much for me as a maternity shot. This is a classic example of the straight on shot not defining the baby bump - if her hands weren't brought together under the belly I probably wouldn't have thought "maternity" at all. The lighting is a bit flat on the white shirt of the belly, so you don't get much bump definition, and combined with what I am assuming is her naturally rounder face this shot just makes her come across at first glance as being a bit on the heavier side, not pregnant. On a non-maternity note, it looks like it's tilted a smidge CCW, which works against the pose (which we intuitively feel should have them leaning to the right).
Shot 3) This is the exception I mentioned. The elastic under the bust, the fact that she is holding the dress against the bottom of the belly, and the light gradations from left to right all amply define the baby bump. There's no need for so much dead space on the right while cramming her against the left (and cutting off her arm), but other than that compositional suggestion I like this one.
Shot 4) Another cute couple shot but even less suggestion of her belly. The facts that she is sitting down, that much detail is lost in her black dress, and that she only has one hand "under" her belly all hide the pregnant belly definition.
Shots 5 and 6) Yes, the "hands as heart" shot is cliche, but there's a reason for that - parents to be like it. I don't feel it works all that well here mostly because of the bottom of the dress hanging loosely off the belly. Had it conformed to the whole belly as in shot 3 I think you could get away with it (put her in a fitted tee shirt, for example). But since you're shooting from the front you don't get definition of the front curve of the belly and because of the draping you don't get the definition of the curves of the side of the belly.
From a technical aspect they look pretty good (exposure, etc), I just prefer maternity shots to really emphasize the curve of the belly.
