Well if we look at the force unleashed (which we shouldn't, since Ady says no to EU) he says he was never planning on taking out the emperor with the apprentice. So it could be said he knew before ANH that he had a child. Leia obviously wasn't "discovered" untill ROTJ.
The emperor must have known Padme was Preggo. He must have known as long as Anakin did.
Right? :?