Yes in the lore but that's the whole point of this thread, my initial comment is "still in horse form" well I would hope so! Can you imagine having an entire 8-legged foal coming out of your human butthole???", I was addressing what would happen if he didn't reverse back before having Sleipnir. The debate then shifted to which holes babies come out of, but we were still in the initial hypothesis :)
Human form doesn't necessarily mean a human MALE. Loki took female form as well, he was basically the Zeus of the Norse pantheon when it came to the length he went to in order to get laid.
Loki is also the parent of the serpent that inhabits Igrasil the World Tree, and the world devouring wolf, and Hel herself, among others. His escapes are many and varied.
or, looking at the whole story and not just the snippet here, he took one for the team. loki does a lot of shit but he does a lot of awesome stuff, too
I'll have you notice that I've also never seen a guy give birth to a horse.