Twilight Sparkle, Fluttershy, and Starlight Glimmer all became pregnant within quite a close timeframe (Twilight first, then Fluttershy and Starlight). Because of such, the three bonded over their soon-to-be colts and fillies, discussing their impending motherhood, and studying up on the best care for baby.
Of course, once the three little ones were finally born, they were all practically raised together since. They’ve experienced quite a bit together, learned a whole lot, and have a big future to look forward to.