Nephilim

When Castiel discovers that his human soulmate is pregnant with his child, he must protect her from the wrath of heaven all the while dealing with the fact that he has sired an abomination.

As the due date nears, Cas realizes that to save his love from his angelic kin, as well as the hybrid growing inside her, he must take away the one thing his wife has always wanted. He must destroy the child.