The real evil behind this (spoilers)
This reminds me of an old X-Files episode where a demon (Campbell) was trying to have a baby with a woman.
I believe that the demon in this film was the father. He was even dressed as the devil in a photo of the two of them. I believe he made fun of religion at one point in the film? He wanted a baby with a woman but this made her crazy in the process. In the end we learn that his current girlfriend is pregnant. Anyone else think this could be it?