The Seated Triangle
Straight ahead maternity poses tend to be more difficult than those from the side. The pregnant profile is immediately identifiable and the lines and curves are easier to compose. However, there is something to be said for capturing the belly the front, both so you are working with a variety of options and because the circle (or oval) of the belly can be well hilighted.
This particular pose has a formal, geometric advantage, especially when posed correctly. It creates a symmetrical form and creates a classic pyramid.
If you are just starting out in photography, you are probably trying to avoid centering your subject, but here it can work very well. Making sure the pose and angle you choose create a strong, clear shape. While lighting is always important, it is more important in any straight ahead pose because it defines the shape of the belly.
This pose also has the advantage of hiding the butt and thighs and is more effective in late pregnancy. As with most poses posture is important.
There are a good number of variations to the arrangement of hands and the gaze of the mom-to-be.
This is an ideal pose in which the subject may lift her head up. It is an excellent way to highlight a good neckline, and it eliminates any double chin issues that could be present in other poses. Palms up, eyes closed, as below, this pose has a peaceful, strong grace.
Leaning back on the hands in this pose tends not to work when viewed from the front because the hands are truncated. A 3/4 rotation or a profile view, however, will work because the viewer can better read the pose.
Finally, for mom's to be with good flexibility, it is possible to vary the pose as below: