This seems like an issue mentioned before where zois would get pregnant but not show it / being unable to give birth (this is one of the post about it), among the known issues it is noted the bug where zois can’t give birth, I wonder if that one is the one you are experiencing!
Could you please kindly share your specs and whether you use mods or not?
Thank you as always
Known issues: [
Pregnant Zoi may intermittently fail to give birth.
→ This issue has been partially fixed, but it may reoccur under certain conditions. Please report it if you continue to experience the problem.](April Known Issues (Updated 04/16))