Agreed with dicetomato. They will find out eventually, no matter how hard to try to keep it from them. Might as well tell them (instead of them finding out from other ways), and ask for advice, and also admit that you screwed up. If you knew you would have this much trouble telling your parents your girlfriend is pregnant, I'm going along with everyone and saying you are an idiot for not taking any precautions (though, if you did and they failed, I retract this statement).