I don't think I ever told my mother, but I'm not sure. If I did it was a long time ago and her reaction wasn't memorable.
I told my father a few years ago, and he wasn't particularly accepting. Sometime in the last year, he sent me a birthday card with my male name in it. That is major progress. The card was in the shape of a football, which was so over the top cliche boy-associated that it made me laugh, but it was a huge relief.
Neither of my parents seemed to have any knowledge about transgender/transsexual people before I came out to them. With your own, you might have to give a lot of wiggle room for possible innocent ignorance.