I was more asking why you decided that it'd work for the ending at all, but that makes sense! And a fertilization animation without showing the pregnancy till the end wouldn't work when the player can take their sweet, sweet time actually beating the game.
I'd ask if having a pregnancy debuff before spawning an ally after some time would be a good idea... except the game's not balanced around that and it'd be a lot of work to appease a niche section of your fanbase.
Still, really hyped that you decided to consider it for the ending!