I think it's entirely up to you and how you feel when you get your BFP.
When pregnant with DS we were so excited and told close family and a few close friends straight away. I was close with my manager at the time and also told her asap. It was fine and very exciting and happy time.
For some reason we decided not to tell anyone during my 2nd pregnancy. I told my mum and sister but that was it. Then I had a miscarriage at 11.5 weeks and was very unwell, admitted to hospital via a&e. I needed support from family and friends, help looking after DS and was signed off work for 2 weeks so had to explain my absence to my boss and other concerned colleagues and I decided to be honest. So in the end, everyone knew anyway, and I actually needed a lot of support and was hugely grateful.
I am pregnant again, and have decided to tell those people that I needed support from with the miscarriage. My close family, a few friends and my manager (but not other colleagues). I am going to wait until we have had the 12 week scan before we tell wider family and other friends/colleagues.
It definitely helps to have some people know so you can have support of u need it, and that's not just In case it all goes wrong. It helps to have people understand if ur not feeling well, if you need time off for scans/blood tests etc. And also - it is lovely to have people to discuss it with, to plan things and to get excited.
But just wait and see how you feel when you get ur BFP. Good luck 