I’m actually in the process of checking through a bunch of games on Itch to see which have it, so I can probably give you a list in like 2 weeks?
As for what I’m actually looking forward to… If done in regular gameplay it could be implemented as a defeat scene or as a reward?
If it’s a defeat scene there’s a few ways to implement it. One is having the mc get pinned down and mating pressed before having a pregnancy debuff applied, being allowed to start moving and fighting again until they eventually spawn another enemy in an animation. Either enemies can’t interrupt it or they force a blowjob and clitoral orgasms during the birth, and the resulting enemy has either the father’s traits or a mix of them and the player’s.
Alternatively, it could be a game over animation where the pc gets dragged off to get chained up and knocked up in an animation with an ending screen of them being pregnant.
If it’s a reward, imagine grappling a downed enemy to make them knock you up. It then continues like the first idea above (debuff, birth scene foes don’t stop like it’s an ult animation), and then you have a lil’ helper fighting by your side.
You could also implement it as a plot thing, where the mc or other characters get knocked up at certain points and the gameplay changes long term.
There’s no one best way to implement it, it’s ultimately up to you how you want it done.
Also, by 3d games I’m guessing you don’t mean VNs with 3d graphics?