How to tell your parents

Hey guys, I know this isn't a common question that people ask but, I promised my mom a long time ago that before I have sex with my boyfriend of almost 2 years now that I will tell her and she'll take me to the doctor to get birth control, I'm really comfortable with my mom and she understands me, but we never talk about personal stuff with me and my boyfriend, did anyone have to talk to their parents about having sex? Bc I am not sure how to bring this up to her bc I'm planning to bring it up to her in October! 😊 please help 😭