Hello!
There are few things that can impact those lines:
- You need to enable the pregnancy system in the game options
- You need to be corrupted enough to have the choice to use a slime or not (you need 1500 or more to have the choice)
- If you don't have any slime, by default you won't use one and might have chances to get pregnant
- In version 1.3 and 1.4, there is a bug that prevents you from getting pregnant (even if you didn't take a slime) if you are too fertile (it will be fixed in version 1.5) ; so you might need to keep a "normal" fertility (which make pregnancy chance quite random)
- Some scenes don't offer you the choice (yet). Only the camping scenes (with a bug in one of them which will be fixed in v1.5 ,were it says your companion used a slime, yet you have the choice afterwards which will be what will be taken into account) and the seduced monster in the tower of gods can make you pregnant
I'm planning to make a small wiki or a walkthrough (though I have no schedule for it yet), which might help answer those questions without having to wait for me/someone to answer