When do you tell everyone

Sarah • Happily Married. Mother of two children, Anthony and Alexis. I'm a Respiratory Therapist. Life is very busy!
The first time I was pregnant was 10 years ago. I was only 19 and I told everyone right away. I was lucky everything went ok. Now I know you should wait just in case.
It really sucks because my brothers gf was pregnant and was about 5 weeks along and miscarried. Now I'm 4 weeks and I know she will be so upset due to just losing her baby. Any advice?