Twilight and Applejack have been married for two years now, so it's not surprising when Applejack gets the motherly bug to have a foal. To please her wife, and to have a foal that belongs to both of them, despite mares not being able to get pregnant the normal way (obviously), Twilight creates a spell to do the job, and it works perfectly. However, there are unexpected consequences when each one of the mane six wake up the next morning and find that they are all expecting their own little bundles of joy.
*Takes place about five years after current cannon*
*Yes, the library is the setting. I'm in careful denial of the thing ever blowing up in the first place*
*Coverart by Me, using a base from Softybases on dA: