Interesting question, I've wondered about this myself a few times and would probably go with human woman willing to be impregnated in exchange for wealth, power...etc. This seems to be a common theme in many of the seventies horror flicks I've seen (though I recall that in one of the Warlock movies the fully grown antichrist bursts out of some poor unsuspecting womans abdomen Alien style). Though I do like murasaki99's idea.