It sounds like you just haven’t bought the nursery. You’ll need to buy the Nursery to keep babies, and that will also unlock the dimensional crystal to adjust pregnancy speeds and even get babies with higher starting stats!
The guild rank dialogue regarding the nursery is Vanilla. I may have to change that if it’s confusing.
Let me know after you try it!
Edit:
Also note - Pregnancy Changes are done via a conversation with the Head Girl or any Slave with Magic Affinity over 4 (only they can magically alter the crystal) after it’s unlocked to at least level 1.
