Kassaz commissioned this artwork and wrote this short story to go along with it, also available in this anthology:
https://www.fimfiction.net/story/569242/2/tiny-stories-with-huge-pregnant-ponies/heavy-herd

A group of ponies is called a herd. Any ponies will do, but a herd is especially a group of Earth ponies. Always the most numerous of the three tribes, these and other thoughts were on Mrs. Cake’s mind as she made her way around the kitchen. She had been thankful for the wide open spaces during her first pregnancy with the twins. Turning her head and looking back at her body, she was especially glad for it now with however many, although the entrance to the kitchen was getting awfully narrow. There seemed to be an old Earth pony rhyme about a baker mare and her baker’s dozen, just like her, but she couldn’t remember it now. Her old apron hanging on the wall caught her attention for a moment, and she chuckled. Wearing that tiny thing was out of the question these days. If she really needed to help, and getting really messy were a risk, she could always throw a blanket over her back and make an apron out of that. For now, she only wore a bra; hers was milk that didn’t need to get into their goods, at least not those meant for their patrons.

Her attention went back to her work and to the other pony in the room, the stallion who had done this to her and the love of her life. Carrot had been working so hard this past year, even getting some extra work elsewhere after the baking at times, while she and Pinkie ran the shop during the day. Housing and feeding an entire herd wasn’t cheap, but they’d manage. Cup Cake noticed a few crumbs stuck to her muzzle, and reminded herself that it wasn’t cheap keeping that dough rising before the buns were finished either, but she reminded herself how fun it was getting the starter ingredients in place, as she ran a tongue along her lips. She blushed, and glanced at Carrot to see if he had seen her or not; he hadn’t, her poor dear too busy for anything like that right now.

She grinned, and looked at the counter again. She was just glad she could still help. Fortunately, Earth ponies were gifted with more than just fertility, and she had the strong frame and muscles to carry her herd and more. She didn’t know how unicorns could manage when they got so big. Unlike her last pregnancy, she could swear she were carrying mostly Earth ponies this time around. The very strong kicking she constantly felt was evidence of that. She glanced at Carrot again. Her strength would help her pin him to the wall again later—and not that she needed it—but that was one advantage of her extra weight too. Perhaps it was too hot in the kitchen, and her demeanour wasn’t at all helping. She loudly exhaled before grabbing an icing bag in her mouth and continuing with the fancy designs for a foal’s birthday party. She smiled as much as she could with her mouth full, and thought about celebrating a certain very large birthday in the future.

The doorbell rang, and she looked to him to decide who would answer, but Carrot set a fresh tray of cookies to cool on the counter and was out the kitchen door before she could even set the icing down and shuffle herself around. That decided, she finished the little designs and dropped the bag back on the counter. She thought about taking some rest, feeling just a little shame about not helping more, and then that rhyme came back to her. She sang it gently to herself as she waddled around the kitchen looking for something that needed doing.

Good mother mare,
sat in a chair,
to give her poor hooves some rest.
Foals in the way,
try as she may,
standing again was a test.

She giggled once she was done singing. She just thought that rhyme to apply to her during her first pregnancy. Now she threatened to break the chair if she used it. She could swear there were one about stairs too, but it eluded her. She certainly couldn’t use the stairs anymore.

Try as she might, she couldn’t find anything that needed to be done. Her attention turned to those fresh cookies.

-

Mr. Cake walked back to the kitchen to fetch the batch of cookies, which wasn’t there anymore. Guilt was on his wife’s face, along with a new layer of crumbs.

“I guess I’ve had a little much.” She didn’t look him in the eye.