I have just made some searches, and yes the term gravid is a 16th century word derived from the latin word gravidas meaning 'burdended' or heavy, so you are right if you are an egg layer or a live bearer you are burdended with a load. So it seems the latin influenced the nordic language in This example.

The term pregnant comes from the latin Prae nasci meaning ( be born) so i Can see the idea of using both words for the method of gestation and birth in animals.

I wonder who first made the choice to use the distiction of words, is it for All the animal kingdom or just reptiles. For example some sharks produce life births and some egg sacks ?

Am i opening a Can of works here!