Go play season 5, dude. Or, here, I'll save you the time. Pulled from my speedrun playthrough videos available here:
#29,171
As you can see, in v0.89.8 - Jennifer's stomach is "flat."
In v0.95.7 - Jennifer's stomach is bloated. Both Peter and Mary wonder if Jennifer is pregnant, but she does not give an affirmative. Players also witness her having conversations with Maria, her dominatrix, about her not being able to hold it in much longer and that she needs relief. Relief is finally given (in the enema scene labeled as "scat").
From that point on her stomach is "flat" again.
You can see in v1.07.3 that her stomach is "flat."
Again, the image you referenced that shows Jennifer with a bloated stomach is from v0.95.7 before she shits all over her backyard.
Now, Uberpie may have ideas about Jennifer being pregnant (by her husband at the time of the current Seasons 1-5). Uberpie may have ideas that eventually Peter will impregnate Jennifer. However, in the game - as it stands at this time - the narrative does not support Jennifer being pregnant.
Enjoy your day.