To scared!!

I haven't told my mom that I'm trying to have a baby yet.. I'm to scared she will be mad or disappointed with me. She always brags to people that I'm 22 and I still don't have a baby and says I'm so smart for waiting ( my sister is 26 and has three kids) but she loves my nephews more than anything. Should I wait till I'm actually pregnant (if it ever happens ?) or should I tell her now that I'm trying?