Pregnancy: Girls can no longer give birth until you've met Artifact What does it mean?
Viewing post in Corrupted Kingdoms (NSFW 18+) comments
When you get access to the nexus and visit the girls in those locations you will make contact with the Artifact.
And you need that because the Artifact explains how the pregnancy works in this game which allows you to start impregnating girls.
Things break if you do them out of order, and the girls 4th heart event would override that.