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Original Description:

Cake Fall~!!

Kassaz commissioned this silly little comic and wrote this silly little story to go along with it, now collected into an anthology:
https://www.fimfiction.net/story/564117/sexier-short-stories-with-particularly-pregnant-ponies

The cakes were on the counter in the kitchen of Sugarcube Corner, and the Cakes stood before that counter icing them. There would soon enough be more cakes in the kitchen, and more Cakes too, by the looks of Mrs. Cake, who had two new Cakes in her belly, but whose belly looked like it held many more cakes than that. They complemented each other in their work, with Mrs. spreading the right icing in the right place with the bag held gently in her mouth, and Mr. sculpting it and spreading it around evenly with the tools held tightly between his teeth. It was actually a problem for two Earth ponies to work so happily with one another, since they regularly took short breaks to glance lovingly and smile at each other, so it was only a matter of time before Cup Cake smiled so much she lost the grip on the bag and dropped it, which knocked a cylindrical container of sprinkles off the counter and rolling away from them along with a cup measure that clanked across the ground in the same direction.

Mr. Cake started to set his instrument down, but she interrupted him. “Oh no, sweetheart, I know I’m big, but I can still get it.”

Carrot Cake wanted to help, he really did, but she turned her tail towards him and then he only wanted to look at six more little cakes that needed icing instead. One of the objects had rolled partially underneath a drawer; she bent her forelegs to reach it, and her belly scraped the floor. He started to chew his bottom lip.

“Now let’s see where that cup went, Cup.” She giggled a little at her pun, and her tail moved back and forth absentmindedly, eventually uncovering her bottom. Carrot wondered if she were purposefully teasing him or not. He had half a mind to mount her if she kept on, it wouldn’t be the first time they’d made love in the kitchen, but a gasp from her broke him out of his dirty thoughts, especially as it changed into a much stranger noise.

He could see why. It had been a secret between them that their twins weren’t going to be Earth ponies but, of all things, a pegasus and a unicorn. Her belly was stretched out slightly on her right side by a pair of wings. He started walking over to her, only to trip and fall hard on the ground, chin parallel to the floor; he knew what that sensation around his hoof had been and, now with a much lower view, he could see the small glow of a unicorn’s horn emanating from Cup’s belly too. It seemed both of them were awake.

He stood, and rubbed his sore chin with a hoof for a moment, before more carefully finishing his walk over to her. “Here, help me sit down, sweetheart.” Her poor legs must be sore after bending like that for so long. He stood beside her and she slowly started to tilt herself in his direction; he braced himself to resist enough to slowly ease her onto her side and, after some noted discomfort, onto her back instead. She propped herself up with a hoof, resting against the drawers. “Oooh, I think it would be easier to lug around two Earth ponies.”

Carrot’s sore chin aside, he had something reassuring to say as he nuzzled her. “Maybe, sugarplum, but remember what the midwife said: Earth ponies can kick hard enough to break ribs.” She did relax a little at being reminded that stretching wingspans and magical surges were a bit easier to handle over broken bones.

The faint glow was still there, and she could see the bump causing it just underneath her skin. Cup Cake thought it funny how she’d long wanted to know what it was like to have a unicorn’s horn, and how now in a way she did, albeit one not under her direct control. The same went for those wings she could feel, but not quite see with how they sat inside her for now, and they certainly weren’t flying anywhere anytime soon. She realized the exertion—and she reminded herself of the kitchen’s heat, which was mild at worst—was causing her to sweat. Sure, she’d put on some weight in addition to the weight of two new ponies, but the longer she stared at herself literally out of shape, and just how cushioned her rear sat against the hardwood floor, the more she wanted to give up and lie in bed upstairs without anypony seeing her like this.

To his credit, Carrot could tell she seemed upset. “What’s wrong, sugarplum? Do you need me to get you something?”

“Sweetheart, am I still attractive,” she stopped looking at her swollen barrel long enough to lock eyes with him, before looking away a moment later, “like this?”

“You’re the most beautiful mare I’ve ever met.” He nuzzled the most ticklish spot on her neck until she giggled against her will. “You’re even prettier than Celestia.” She knew he was exaggerating, but he wasn’t letting up on that spot, so she couldn’t retort yet. “I’m so glad that you’re my wife, carrying our perfect foals for us.” He finally stopped nuzzling, and she needed time to catch her breath.

“Thank you, sweetheart.” She happily kissed him on the lips. “Here, help me up so we can finish these cakes.” He didn’t know whether she meant cakes, or Cakes, but he agreed either way.