Rarity has desperately wanted to visit and network for years—nothing sexual, but she sells a lot of socks to this crowd and wants to see how she can expand that business—yet has never been allowed into the backroom where only VIPs (Very Important Ponies) are allowed. She loves her son, and figures since he’s making use of her organs right now, she can make use of one of his. Technically, they’re one pony!
The mares in charge of Club Futa are probably going to change their rules now that Rarity’s pulled this little stunt, but she definitely meets the technical definition; they even took an ultrasound to check.
It’s not the most nerve-wracking faux pas Rarity’s committed in her life.
It’d probably translate better if there was an x-ray alt, but using her unborn son to try and as a futa on a technicality is one of the most unhinged concepts I’ve heard of in a while so kudos to the commissioner.
I’d imagine Cold Blooded Twilight did it that way so a censor bar could go on Rarity’s belly.