9 drops of eucalytus oil can kill a baby (can't remember where I read that), so I don't know that it would be great for an unborn baby & what goes onto the mother's skin get to the baby.
I'm not exactly sure about that either, but e oil is very volatile and should always be kept out of reach of kids. Should also be kept away from direct contact from mucuos membranes as well.

Although these things are natural, they are also powerful