To be clear the pregnancy mod increases the size of the girls stomach to appear pregnant, there is no actual "pregnancy" in the game. The girl will not get pregnant and have children no matter how much you have sex with her.
This will be the final answer, very clever LoL xD
But yeah, THERE IS a pregnant effect mod, that make the 3D render models to seem they (it) are pregnant, only in the shape, no in other symptoms or mood.
If tou are getting nailed them so hard, and you wish to get them pregnant with a rounded belly in that very moment, I think that never gonna happen, nor in the game or in real life, although it may be a "cumflation" effect that I've never used before, in when the dick is so massive that the belly seems to be like a plastic bag every time the dong go in and out.
So.
Number one: YES, there is a pregnant mod that make the belly rounded like pregnant.
Number two: AFAIK there are no "Instant" pregnant after bang your model in a H scene or action, But maybe there is a cumflation effect when that poor models get nailed with a horse benis or so