I will be waiting till my first ob appt( around 8-9 weeks). As long as the heartbeat sounds good your chances of miscarrying are slim at that point. I am on my 3rd baby and already have a little bump( I am very small) so I cant keep it secret for too long.
We're doing the same type of thing. We've told the grandparents and I've told just a few of my closest girlfriends that have been praying for us through this whole adventure of trying to get pregnant... the rest we'll be waiting til 12 weeks to tell.
We told our parents and siblings right away (I'm just not that good at containing it, lol) but we are waiting to tell friends, co-workers, etc. until 12 weeks. This is because if I happen to miscarry, I will need my family for support, but I'd rather not have my friends and other people feeling sorry for me or asking questions about the baby, not realizing that I'd miscarried. But hopefully that doesn't happen!