what Arnie should have done
To the best of my knowledge, a pretty sure method of not getting pregnant is to be pregnant already. So wouldn't an effective and relatively painless way of thwarting Satan's scheme have been for Jericho (or any convenient male) to impregnate Christine before Satan could have his evil way with her? Dammit, for the sake of saving humanity, I'd even have been prepared to do the deed myself. Heroic self-sacrifice, I know.
"I beseech ye in the bowels of Christ, think that ye may be mistaken."