Who are you telling when?

Heather
Whee! First post! 
What's your plan for when to tell certain people?
I had to tell my boss early because of the chemicals we use to clean. Then I told my mom, my sister and my best friend shortly thereafter. I figure that if I do miscarry, I'll talk to them about it anyway so there is no harm in them knowing. 
My MIL will find out after the first ultrasound (DH's choice)
Other than that I plan to announce at Thanksgiving but I'm not sure I can keep it to myself that long