I was wondering if anyone here knows of any sprite sheets of pregnant women like the kind that would be used in a 2.5d DOS game.

Sure, there's a really excellent free RPG maker game by the very talented HarlequinGemini called OkuSim that features pregnancy, though it's secondary to stuffing. There are five playable wives. You can download it here: 

https://forum.weightgaming.com/t/okusim-...ator/22584


Here are its sprite sheets.

Thank you, but this isn’t really what I was looking for. I was more referring to the 2.5 sprite style that you would see in games like Doom, Ultima Underworld, Duke Nukem or the old Elder Scrolls games.
 
That RPG maker game does sound interesting though.

Not to my immediate knowledge but it wouldn't be too difficult to replicate the same processes that they did back when. Doom used hand sculptures and toy guns, Mortal Kombat with actors, and many later games used 3D renders. Daz3D and pixel filter work wonders for this. Heck of a lot cheaper and less time-consuming than drawing everything by hand like they did with Wolfenstein 3D. 

This was a test I did several weeks ago throwing a 3d render into a pixel filter online. Granted it would still need a lot of post-work before it is game ready, but it would serve well enough as a base image to work off of. All you have to do is repeat the same process for each frame of the animation and align it into a proper spritesheet.

(Base image, 64x64px, 48x48px, 32x32px)