Trixie's Baby Trick: The Sequel~!!

The backgrounds used can be found here and here.

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/564117/8/sexier-short-stories-with-particularly-pregnant-ponies/trixies-baby-trick-the-sequel

“Beg.” Twilight Sparkle said it again. She sat on the floor, looking down her nose with a smug expression on her face to accompany her crossed hooves.

“The Great,” Trixie huffed, “and, and Powerful,” she grunted, hoof moving in small circles on her body in vain, “Trixie... does not beg.” Trixie sprawled on her side against the ground before Twilight, trying her absolute best to maintain her showmare’s image. The smug mare who had so skillfully transferred Twilight’s pregnancy into her own body for show was no more; she was replaced by a tired mare who had now been pregnant long enough to feel the various aches and pains spreading into her core with no relief in sight. Her magic pulled her mane in two directions and tugged on her tail, but her horn wasn’t lit. She was feeling blows in places she didn’t ever expect a hoof to reach. When she could adjust herself, she traded one sore spot for another. She couldn’t even cast her magic right now, with a headache forming.

-

Trixie had yawned and stretched her legs as she awoke, opening her eyes to see two very angry parents staring back at her. Trixie’s belly had been full for the first time in a long while, and seeing it in her peripheral vision had reminded her that it wasn’t only food in there. Twilight Sparkle had assured her husband that she would handle things, and he had left them alone.

Trixie hadn’t expected the barrage of medical devices Twilight had used all over her bump, so it had surprised and frightened her to be lifted up in magic and set on the floor before the purple unicorn got to work. A tape measure around her swell and a very cold ear trumpet set on every part of her belly had turned it from quiet globe to restless protrusion. Every time Trixie had started to return to the dream world, Twilight placed some instrument somewhere sensitive. Each time gave her a jolt, particularly when Twilight had taken the ear trumpet—still somehow just as cold—and nearly placed it between her hindlegs to listen in at her belly’s backside; that had caused some yelling. Then the prenatal magic started.

-

Trixie wasn’t afraid, at least not while she was still pregnant, but she was certainly annoyed by this point.

“Your problem, Trixie,” Twilight smirked, “could it be that you’re not magically strong enough to carry my foals?” Trixie continued to glare at her, just barely over the big blue belly between them. “After all, any unicorn should know that foals tap into their mother’s magic reserves, it’s basic knowledge! Any mare who casts “gestation translation” on a more powerful unicorn would have a terrible time carrying foals attuned to their true mother’s magic levels. Why, that would be very draining, literally, not to mention that they’d cast spells outside the mare’s body more easily, and furthermore-”

“Enough, Trixie needs no lecture, Sparkle.” Trixie looked at a spot on the floor and grumbled. “The Great and Powerful Trixie merely has a tummy ache from all she ate last night, nothing more!” She locked eyes with Twilight again, and cleared her throat without blinking. “So, what exactly do you suggest Trixie does? She can’t—she’s in no mood to cast the spell again right now.” Errant magic pulled the brim of her hat down over her eyes, and she pulled it back up by hoof with a very angry expression on her face. With gritted teeth, she looked at the big blue ball jutting out from her with a look of hatred; never before in her life had she been so upset with her body.

“Oh, you don’t need to do anything, Trixie. After about twelve hours, it’s safe for another mare to cast the spell, slowly.” Twilight almost began to list the negative effects of just that, but closed her eyes and figured she’d let Trixie learn about them first-hoof; she took a deep breath, and cast the spell. Trixie’s eyes reduced to pinpricks as she felt her guts rearranging themselves around her shrinking womb. Twilight stayed perfectly still while she cast the spell and felt her belly burgeoning outwards and against the floor. When the spell was nearly finished, Twilight cracked open an eye; Trixie’s face was green. After a hoofful of moments, everything was as it had been before Trixie’s trickery. Twilight slowly exhaled, and had no trouble breathing because of the air she’d used to reserve space in her body for her lungs; she felt the familiar stirrings of life inside her once more, and set her hooves on her belly with a big grin. Without her belly propping her up, Trixie rolled over and fell flat on her stomach, her face too.

Twilight slowly pushed herself up with her hindlegs. She was no dancer, but it was easy to stand on just two legs with such a balancing force already resting against the floor. She got her forelegs back on the ground and started to slowly tilt her body back-and-forth to let everypony settle back in. “It feels so good to have my motherly figure back,” she looked at Trixie’s rear, perhaps smaller than it had been, “and thank you for any additions, Trixie.” She walked across the library to the front door, looking back at herself once she was finished. “I love you, my sweet little foals, back in my belly where you belong for now. The next time you get out will be the real thing, okay?” None of the prenatal magic was currently strong enough to leave her body, but she’d need to put on some magical dampeners soon, after Trixie left. She looked out the front window to her husband, working on something related to the property while he waited. She opened the front door and spoke to him. “Sweetie, we’re all done in here. You can come escort Trixie out now.”

A voice, shaky, replied behind her. “The Great and Powerful Trixie is going to vomit.”

“Go be sick outside.” Twilight didn’t look back, and was rather glad she wasn’t looking when she heard Trixie vomiting all over the library floor. It seemed Trixie didn’t get to keep any of the free food after all.