This is some research I did on how to clearly work out the shape and proportions of a pregnant woman and her belly. Here are the notes I made that can help you with your drawing in the future.

1: The bump is formed around an egg shape, facing upwards during the first few weeks and downwards during the last trimester. And also, the middle section of the body makes up a triangular shape, from the sine to the top and bottom parts of the belly.

2: The front and back create a sort of pattern going from the bottom of the butt cheek to the back of the neck, on either side of the body. The rest of the figure can be worked out from these two lines, like the breasts, the leg, the ribs and the butt.

3: The belly should curve on the furthest point from the egg shape and not go all the way round. Make shore that the belly conects to both the croch and the bottom of the breasts.

Image used belongs to its repective owners.