Sugarlys - it can be a risky thing, but keep in mind the chances of something bad happening are pretty low. K's brother and his wife told people at 2 months and at 10 weeks she unfortunately miscarried. She told me she hated everyone knowing and asking how she was, so the next two times she was pregnant they didn't tell a soul till 3 months, and both babies were born healthy and amazing. It really depends. If you only tell close family and god forbid something were to happen, least they can be supportive for you. That's what I did, only a select few. Now that we know things are great, I plan on telling K's extended family on Sunday and then we'll announce to the world of facebook so its out there.
Good luck, no matter what you decide I know it'll be right for you.