telling my mom I'm pregnant

I just found out today I am 4 weeks pregnant. I am 18 and my boyfriend is 20. We both are in school and work and we live together. Could someone please help me figure out a way to tell my mom? She was so against me moving out to live with my boyfriend. She's the type of person that if I tell her I'm pregnant she would yell and tell me my life is over, I'm not gonna be able to finish school, etc. really any bad thing you can think of. Help please