With our first we waited until I was about 10-11 weeks to tell most close friends 0 I was 12 weeks when I told work, although I did tell my boss earlier as I'd had a m/c earlier in the year and wanted her to be aware. We told family pretty much straight away!
With this one - my DH is just beside himself and was telling people before we even knew when I was due! I could have been 2 weeks at that stage! Luckily I was about 7 and a half weeks. We have now pretty much told everyone that is close to us. I think its up to you, I think even if something happens, in a way it's easier if those close to you know as you don't have to explain things - they already know if that makes sense. Good luck!