This model is perfectly capable of generating both SFW and NSFW images, such as characters that are clothed or nude, but this also depends on what kind of clothing you decide to use, now reason why I am pointing this out is because there will be times where if you try to generate an image with a said character that is supposed to have clothes on to have missing sections of clothing, that is if you plan on making your character the size of planet earth.

Just know that this model only handles pregnant bellies, not breasts or any other body parts of any kind.

Remember that the pregnant belly size on a generated image will depend on the width and height of the said generated image.

Base Model = Illustrious (though you can use others if compatible)
Clip Skip = depends, but either 1 or 2
Steps = I'd recommend 25 or 30
Guidance = A range of 4 to 7 idk
Strength = 1.0 recommended, experiment with strength values as needed.

Very basic trigger words:
pregnant, big_belly, huge_belly, outie_navel