My mum actually knew at 5 weeks, about 3 days after we found out.
She rang me up at work and said 'your pregnant aren't you, why didn't you tell me!"

So then we had to tell them, and DH's mum. But we didn't tell anyone else until 12 weeks.

It was actually good that I had her to talk to, as I had a couple of scares etc and ended up having my firts u/s at 6 weeks.