There should be a cute pixel-art video game where the character you're trying to romance suddenly pauses mid-dialogue, groans, and touches their lower back on either side, right above their hip.
You then get a different view of what's going on inside them: the egg trying to pop out of their ovary, which you successfully watch it do.
When the game "pulls back" you're like "what's wrong?", and they're like "hah, hah, uh, nothing - just a weird ache. Let's keep going." Or whatever.
There would be guides you could find to help you time sex with them (if you haven't progressed the romance into the actual romance, and past a certain point for that as well, there's a walk-through for how to rape them [and a walkthrough for the dialogue tree to manipulate them into forgiving you]), because there's a very limited time of day each day, for a certain number of days after ovulation, during when you can impregnate them.
And there's a trigger minigame where you have to hit the prompt at the right time if you want to sleight-of-hand that you are using a condom when you aren't really, and an additional minigame where the Hero sperm in your load has to dodge cervical crypts and the like, and navigate to the egg so it can be enveloped.