Congrats!
Having gone through 4 miscarriages myself, two before each successfull pregnancy. I would recommend holding off on telling anyone until you are past 12 weeks. I think I may have been a bit superstitous too as a result of what I went through.
JMO....
I felt horrible when everyone knew I was pregnant and then miscarried.
When everyone knew then they were all calling me offering sympathy...etc and that was really the last thing I wanted at that point was to talk to anyone. I didn't want anyone's sympathy, I just wanted to be able to have a baby.
I have a good suggestion on how to tell your Mom..... Send her a Mother's Day card that reads Happy Mother's Day Grandma.
I even held off on telling my husband for a few weeks as I didn't want to disappoint him again. But at around 8 weeks pregnant Father's day rolled around, so I sent him a Father to be Card for Father's Day, that is how I told him.