Without having read the particular Jataka you are referring to, I am pretty sure that this series can shed some light on your question.
The theme of being in-between two states is a recurring one in mythology in general and in some Jatakas in particular. Being suspended between heaven and earth is one variation of it; maybe being born between the father’s and the mother’s place another. I remember one Jataka (can’t tell which one exactly) where the child is literally suspended in the air, between heaven and earth, and this happens exactly between mother and father.
According to tradition the Buddha’s mother is giving birth while standing, so in this way too the child is suspended between heaven and earth.
Highly interesting talks!