I am 7 weeks pregnant after 2 losses and I totally share your concern.
I have told my mother, and my 2 best friends but no one else so far. As it was, my mother posted on my Facebook "Thanks for the exciting news" and I had to whip it off before anyone figured it out (Hopefully). She is pretty hopeless with a) keeping her mouth shut b) understanding that ALL of my friends see her posts to me.
We haven't told the in-laws yet and probably only will after 12 weeks. They don't know about any of my other pregnancies or losses either as they are just not that good at understanding and supporting the harder stuff in life. They tend to want to brush over everything and say things like "Oh well, try again."
My husband did blurt out to his ex and his son last night on Skype though, which I felt really funny about. I absolutely love them both and we are all very close but I just don't want too many people knowing and getting all excited as I hate the feeling of letting them down if things don't work out.
I just HATE PgAL for the fact that I can't just be excited and want to share the news!!