talking to mom about sex

have any of you ever talked to your mom about sex? i lost my virginity and really wanna talk to her about it but it was just a one time thing with a guy not a boyfriend or anything. i don't want her to be mad at me or judge me. we have a really good relationship and i'd feel relieved talking to her about it but i'm just not sure how she's going to react. i know she was 18 once and probably did worse but how should i go about bringing it up? thanks!