For my first i didn't tell anyone other than DH and a few close friends until 18 weeks. At first it didn't seem like I really was pregnant. It took me awhile to come to terms with it myself. Then I just wanted to keep it special and secret for us. I kept avoiding talking to one of my friends because I knew I would blab as soon as I talked to her.
With the second it was similar but I didn't feel the need to keep it secret. I was pretty excited from the beginning but waited until 13 or 14 weeks to tell.
Meanwhile DH told his whole side if the family really early both times.