Mary’s gonna abort everyone in that car!

I’m trying to figure out the logic of Mary being pregnant.  Did she really not know what a condom is or something?  Did she lie to Eric about taking birth control pills since apparently he didn’t seem to notice a lack of protection otherwise.  Did he just not care?  Ah well.  I guess the likelihood of getting pregnant when you’re evil and having dramatically hypocritical sex is about 1:1.