With Danielle, we had decided to tell our parents & siblings early on, but then let the rest of the world know after we were through the first trimester. It turned out the news traveled fast, and Adam's brother, Ben, found out we were expecting from his neighbor, instead of us.
Since we had that experience, we said right after that, that with our next child, we would wait to tell everyone until the second trimester. But since our pregnancy with Danni was so public, and people we didn't even know were praying for her (don't get me wrong, we really do appreciate all the prayers), I felt the need to keep the next one to ourselves for as long as we could. We joked that we would show up with a 5-year-old to Christmas one year, and finally tell people.
So far, so good. We have kept our secret, though, we have only really known for about a week. Which I suppose is better than with Danielle, since Adam had told his brother, Jon, the day we found out. (They were up getting the cabin ready for hunting, and I think Adam was just itching to tell someone.)