Coming out to my mom

I have come out to a select few people. When I eventually come out to my parents, I feel like my dad will handle it perfectly well, but my mom will absolutely freak out. She has a worrisome, obsessive, controlling personality, and is a devout Christian. Inevitably, she will think that me being gay is somehow a consequence of something she thinks she did wrong. I know it's coming. Aside from saying "it's not your fault" (which will accomplish nothing), how do I deal with this situation?