With the software I'm using, I don't have any way to make it look like a baby is coming out of her. I don't have an image of a baby that looks like it's made from the same material, and I can't edit her to have a widened birth canal. If I draw a separate image to depict the birth and don't match the model's artstyle flawlessly, it kinda makes you think "hey wait a minute that's not really her" and that sucks. I don't have the means to do justice to the miracle of birth. Sorry!
There's always other games for birth scenes! Hazumi has it, and Liz Tower Breeding Mod has a lot of it. I recommend both