Pregnancy mechanics are tied into gameplay, changing the character's selection screen and lasting a few in-game days thanks to the power of magic!
Each character has an alternate selection screen with a different minigame (mostly milking so far), and a training scene that gives a unique h-scene. Pregnancies are repeatable, though rewards are really only obtained once for each training scene, and the milking minigames don't currently have any rewards at all!
The game is still a work-in-progress, with only 2 girls being mostly complete and the third (out of a planned 4) having only a single scene and nothing else so far, but the first two girls do have their pregnancy mechanics mostly implemented, if still in need of some polishing!