How do I tell my mom I'm pregnant at 18

I just found out I'm pregnant and I don't even know the half of where to start . My mom is my best friend but she's super firm on what she believes about teen pregnancy . My sister and her & my brother had kids young . I don't want to disappoint her . I know she will support me but she's literally my best friend and I don't want to put stress on her ... I'm around 4 weeks and I was thinking maybe wait till im 6 or 7 . I have a scan at 7 so maybe tell her after the appointment or should I tell her now ?? Any advice on how to tell her would be super nice . I don't think Ima gonna do it in person I can't imagine her face . I just couldn't take it . I love her so much & I don't want her hurt but I really need her for this