It happens to the best of us.
Thus uis based on a legend that Loki shapeshifted as a female horse, and ended up getting pregnant. I forget exactly why, though. Feel free to check me, because it's 3am for me
@Invalid User, it was a tale of a bet between Asgard and a man, regarding the building of a wall. The Asgardians believed he could not complete it within a certain time. They were stunned when, with help of his horse, he got real close. So they sent Loki to deal with it. He decided to seduce the horse. So he transformed into a mare, ended up getting pregnant, but succeeded in causing the man to fail. Soon after, Sleipnir was born, and now Odin rides his grandson into battle.
@Cloverleaf, thank you for getting the accurate story. It's pretty great
Unnecessary brackets are unnecessary.
@NameyMcNameFace, [what] [brackets] [?]
Must have happened a lot for her to carry a horses child