Would it be possible to add some sort of everlasting pregnancy? fetish reasons
One example would be: A pregnancy pausing potion leaving them in there currant state till get counteract potion returning back to normal.
Extreme example: Parasite baby base of living armor/suit get from underground ruins; character that pregnant with the parasite never be able give birth to it and stuck with lust gains and pregnancy debuff in battle/belly inflation in exchange for buff of some sort like +25 health, 15% protection/damage reduction or + 1 Magic Affinity(shameless grab for power).
Basically laboratory thing/potion or trap found in underground ruins.