Only a few NPCs can get pregnant by the player, Briha, Zheniya (the zil call girl), and the female raskvel mob. Both Briha and Zheniya will have text telling the PC you got them pregnant, while you just have to be running around the wild five days after sexing a raskvel for her birthing scene to trigger. Assuming you actually impregnated her, even if you jack up your fertility it's possible you won't.
As TayJK said, there will be a status in your Codex's personal screen (right above the belly's stats iirc) that will tell you that you're pregnant, the species of the pregnancy, and the time left before birth.