guy with a size kink gets knocked up by a size shifter. all through his pregnancy, his baby has growth and shrinking spurts the way other babies would kick. it's disorienting and painful. one minute he'll be fine, then his baby will knock him on his ass by deciding to grow as big as a foal, then his bump disappears when the baby shrinks to the size of a peanut. he has no predictability for any of this, and it's made his pregnancy a confusing nightmare. he didn't know this would happen, the dad didn't warn him, and he had to furiously look up sizeshifter pregnancy after an embarrassing growth spurt in the grocery store his first trimester, when baby decided to make him look ready to pop and tore apart his favorite shirt. clothes have been out of the question for months now. his belly skin is so red and stretched out and agitated with the constant inflation and deflation, the baby just getting more active near the end of the pregnancy. he worries about the birth. what if his baby has a growth spurt that makes it impossible to push out? or godforbid, one while he's actively crowning?
Having the baby shift sizes while he's giving birth would be so good, it keeps growing and shrinking rapidly while he's trying to push it out, making his labor so much longer and more painful than normal.
It's constantly changing shape, stretching him wider than his body was ever meant to stretch and getting stuck when it shifts into something huge. He screams and cries, thrashing in pain as he bucks his hips wildly in an attempt to dislodge the massive head, trembling under his towering belly and begging his baby to shrink before it breaks him. When it finally does shrink, he pushes frantically, not even waiting for contractions because he desperately needs to make as much progress as he can while the baby is small enough to be pushed out.
His labor drags on for hours, constantly bouncing back between non stop pushing when it's small and feeling like its about to split him in half and getting stuck when it's too big. He never knows how long each phase will be, he could have only minutes to push and hours of torture stretching around a creature with the head the size of a watermelon, or vice versa. His labor could last days if the baby decides to shift too big too much, leaving him exhausted and barely conscious by the time he manages to get it out.
He feels it slip out with one last push and collapses back in relief, thinking he's finally done, but suddenly his tummy jumps up, swelling right back up until he's even bigger than he started. He screams in pain, watching his belly in horror as it squirms and bounces with movement. It turns out that because shape shifting babies are always changing and shifting sizes, it's nearly impossible to figure out how many there really are. What he though was one baby constantly shrinking and growing could have actually been twins, triplets, or more.
After hours and hours of giving birth to just one baby, he realizes he has to do it all over again, and without knowing how many babies he's actually carrying, he may have to push out many more after that...
