This comic is based on the following short story by Kassaz:
https://www.fimfiction.net/story/526921/9/short-stories-with-pregnant-ponies/the-most-devastating-insult

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Rarity lay on her back, in her chaise lounge, with a bucket of icecream on her pregnancy. A more appropriate spot would’ve been the nearby table, or even the floor, but empty buckets occupied those positions and more, making her resemble a mare who had finished furiously painting. Standing before her was Sweetie Belle.

“What’s wrong, Rarity?” Sweetie Belle didn’t really care, she just wanted some icecream; by now, she was accustomed to Rarity having her episodes, and for the past few months her behaving normally had become the episodes. If she could distract her long enough, she could scoop out some of the icecream before Rarity finished inhaling it.

Rarity started telling some long story about some hoity toity pony at a fashion show. “Then, he, he called me fa-a-aa-a-aaat!”

“You are fat.” Sweetie Belle was blunt.

Rarity started wailing again and, worse, eating out of Sweetie Belle’s bowl.