Spike you better tell her to stop or it will go worse.

I just love the design of their diapers, the checkerboard pattern shows off how poofy they are so well.~ And of course the implication of Twilight casting the spell over and over in an attempt to fix it, only making them thicker, is one I adore.~

oh lordy, Spike looks so good in this artstyle.

Hey twilight don’t those giant diapers feel comfy

But what if there’s a really useful spell in there?

As Twilight casts the spell again, her diaper swells up. Only this time, it is now wrapped around Spikes', at which point the young dragons' own diapers begin to peel away as he sinks deeper and deeper into Twilights' padding.
Despite her struggles to keep her assistant above the rim of her diapers, Spike is soon swallowed up by the sea of nigh-indestructible padding, drifting closer and closer to the innermost layer.
As Twilight is sitting atop her padded rump crying her heart out at losing Spike to the spell forever, she feels something pressing against her as her stomach begins to slowly bloat out and whatever magic holding the diapers together vanishes. Worried about Spike, Twilight peels and tosses away layer after layer expecting to find Spike, only to watch as the final layer coming undone to see the last traces of her assistants' purple tail sticking out of her marehood before getting sucked inside.
Twilight groans as she feels the contractions as Spike was pulled through her birth canal, past her cervix and finally stopping when Spike enters her womb.
A few seconds as her cervix sealed up, Twilight felt something connected to her body as an umbilical cord reached out to bite Spike on his stomach as the young Drake began to shrink down.

Months later, Twilight is now walking throughout Ponyville as she carries a sleeping purple-coated green-maned colt on her back, the residents pausing to give their greetings to the Princess and her beloved son Prince Spike.