It sounds like your cat is trying to tell you to stop touching a certain area. Every time you touch that particular area, she will scratch to tell you to leave that area alone. This is especially true for pregnant cats because they are as unpredictable as many pregnant women who's hormones cause them to eat weird things, or worse. Try to see which area you pet when she scratches and avoid that area in the future. I suggest you also keep your face away from her for the time being. Another thing you can do is play with her with things other than your hands. This might give her another outlet for her temporary aggression.