I told my mom at 5 weeks. She obviously knew about my previous MC, and I needed her support. We told DH's parents after seeing the HB at 7 weeks. We wanted to tell them earlier, but in person, and couldn't before that.
With our previous pregnancies we decided to wait until x weeks to tell them, and we only got to tell them bad news. It was horrible. They deserved a little happiness, even if it would end badly again.
At work, and other family, I decided to tell people who knew about my MC, I would obviously tell them if something happened again, and again my thought was, why not spread some happiness, and I need support, and them being positive and happy for me, will help me feel more happy and positive.
I am so glad I told, I don't know what I was thinking waiting before.
Not everyone knows though
But I am not hiding it or denying it. I'm not showing yet either so that makes it easier to just not tell.