Freeloaders.

One of the major reasons a sovereign was sent to check the pregnancy is to ensure the accuracy of the inquisition. There is little in the lower plane that can hide from the senses of a sovereign.

There are been cases where the ruling patriarchs didn't take the issue of a prolonged pregnancy seriously but later regretted it when the female gave birth to the child of a demon god or demon king. The child grew up to become the vessel for the powerful demon to descend into the plane.

The destruction it caused was more than enough to justify sending a sovereign to check suspicious pregnancies. It is either a momentary discomfort for a sovereign or trouble from a murderous new citizen.