This is so individual, and everyone needs to approach it with what they are most comfortable with. Sometimes our experiences shape us!
For us, pretty much everyone knows through the grapevine...our children always know right away and then they have big mouths
and because by 5 weeks I can't hide it. I'm smaller build and with having lots of children I "show" (I know it's not baby already, but my uterus is already at my pubic bone) early.
We actually don't directly tell people at all, except for the few close family members and friends, because many people we know have a negative reaction, and we don't need their negativity about what we see as a blessing.
I have had a m/c before at 8 weeks and found the support of others to be really helpful. If people hadn't known, it would have been lonely. A few years ago I had a m/c at 13.5 weeks, supposedly after the "safe" time. I figure there are never any givens or guarantees, and I appreciate the prayers.