Last time I told my mom right away (she's an ultrasound tech so I could get a scan right away!), my boss a week later (because I was so sick), and put it in Christmas cards for everyone else (around 12 weeks). My husband told his best friend at mile 22 of a marathon they were running a few weeks before Christmas, ha!
We'll probably do another Christmas card announcement for extended friends and family... otherwise I might just tell folks as I see them. I'm feeling much less concerned this time around--hope it doesn't backfire!