Going back to basics and thinking about knights. There's a lot of lore re: living armour, death knights and such that I would love to introduce some preg kink into.
Like an oathbreaker dying and becoming an undead creature still wearing its past incarnation's armour; they don't have a body as such, and they're mostly held together with pure magic.
Now imagine that oathbreaker dying with a huge round belly that their armour can barely contain. Imagine them rising again, two red lights shining from the slit in their visor the only indication that they're more than a suit of armour. And yet their chainmail is stretched across their round middle.
Are they still pregnant? How is that possible?
Their gravid shape clearly hinders them: the arc of their swinging greatsword is slow and unbalanced. This must be how they died.
The general protocol here would be to send the knight to their second death with a well-timed smite, but this particular specimen is too interesting to just put down.
Disarming them is easier. Pushing them onto their back even more so.
They're unnaturally still; no breathing, no trembling, just a walking corpse. And yet they cradle their heavy-looking belly with both hands.
Your swordhand keeps your blade steady under their chin, holy light casting shadows across the knight's helmet.
The other hand reaches for that irresistable, paradoxical roundness.
You startle. Your hand flies back to your side as if burned, then returns immediately to the knight's swollen middle.
The metal feels slightly warm, and there's movement.
How can that be? You can clearly see the narrow gap between pieces of armour. You can run your finger along the rim of a gauntlet and feel the empty space that would normally contain living flesh. You can look up into the pitch black darkness showing through the visor where two dim red lights stare out instead of eyes...
As you watch, the light grows even dimmer and briefly flicker, almost like it's blinking. Your free hand returns to the bewildering movement, cupping and lifting gently, testing its weight and give.
Your eyes never stray from the helmet, and so you see the precise moment your touch registers: the lights flare, like wide suprised eyes, and dim again, almost to nothing.
You jostle its belly experimentally, and are rewarded with an even bigger reaction. Interesting.
Well, you can't just kill this knight while such a baffling mystery goes unexplored.
Better truss it up and take it back into the city. Let some scholars shine their light on it.
And if, while resting at camp that night, you find yourself petting the knight's belly with one hand down your trousers, who's to know?