Coming late to the party on this one, but...
There's a lot I like about this image. The tones in it work very well together - her skin, the dress, and the seamless are very complimentary. I like the lighting. I agree with tirediron that a hair light could work, and would very much be called for in a typical portrait, but I personally like letting elements away from the belly fade a bit into the background. I also like the rapport she has with the camera - the tilt to her head, her expression, and her eye contact work very well. She comes across as a confident, beautiful woman who happens to be pregnant. Not all maternity images have to be about the bond between mother-to-be and her child-to-be.
There are a few things I'd tweak (that haven't been covered above). IMO the composition is just a bit off. The horizontal center line of the image seems to be right about where her dress separates at the top of her belly. This creates in imbalance in which most of her body is just left of center while her belly is just right of center. I think if the center of the image were where her dress makes a little V in the center of her chest you would end up with a more balanced image (her head just slightly left of center, her belly and leg slightly right of center). Alternatively you could move her more off center (crop from the left), though in this particular case I don't know that the unbalanced negative space to the right would buy you much. I actually think this would work very well as a square crop...
This may be unfair to say, not having seen how the dress drapes in person, but how it hangs over her belly leaves a bit to be desired (to me). From this angle, the near side of the dress looks like it's hanging pretty much straight down, we don't get a feel for it following the curve of her belly. And I wish the far side of the dress wasn't visible all the way down to her hand, that it had wrapped off the far side of her belly instead. As it is we get an artificial curve to her belly - the highest contrast is between her skin and the dress - which makes it almost look like we're seeing her belly in profile rather than the 3/4 angle of her pose. Had the dress fallen off the far side we'd have ended up with belly against the seamless and gotten a better feel for her form.
Lastly, I don't mind seeing her thigh, I actually think the shot would benefit from seeing a bit more of it (see my above interpretation of the shot). This bit of thigh does seem like a bit of an afterthought and does pull from the belly a bit. I think if the dress draped a bit differently, not hanging straight down in front of her leg, it would have seemed more organic. Or, even better, I think pulling back a bit would help. You'd get a bit more of the length of the leg and, as a consequence, move her belly slightly higher in the frame. This would help with the visually low weighting that dasmith232 mentioned.
Overall I really like this, thanks for sharing!