This artwork is based on the following short story by Kassaz:
https://www.fimfiction.net/story/526921/33/short-stories-with-pregnant-ponies/an-ethical-dilemma

Twilight Sparkle lay on pillows, with chalk on her hooves, a scroll in her lap, a foal in her lap, and ink splotches everywhere. “Let’s see: estimated gestational age, length, magical field strength, weight, approximate horn circumference...” The scroll held figures, about her figure, in a roundabout way. “Spike, I need that book!”

Spike had no retort, slowly carrying the ancient tome. He gasped for air as the purple unicorn levitated it while making more meaningless marks on the chalkboard. “You’re—you’re freaking out again, T-Twilight.”

“Hush. I have to know if I can participate.” She flipped through the pages. “I have to know the precise definitions of foal and dam.”

“N-Nopony cares if you aren’t technically a mother this Darling Dam’s Day, please.” He collapsed.

Her stomach growled. “I wonder where hubby is with the groceries.”

“I should’ve gone with him when we saw you measuring yourself with the protractor.”