I am waiting until near as I can to 12 weeks.
My 12weeks lands on xmas day - so I'm hoping they let me have my 12weeks scan before xmas if allowed. I have a midwife appointment on Monday so I will ask then for an actual date.
We want to announce it on xmas day if poss after the scan. So I'd like to tell my boss before then rather than him find out on social media over xmas.
Might tell him the week running up to xmas when he's in a good mood 
I have only been at this job for 1 year and am a manager of a team structured new for me to come in. So I feel really bad and guilty for dropping him in it so soon after starting 
I was at my previous employment for 8 years and the pressure and long working hours were just getting too much. We were having trouble conceiving anyway, so after the GP told us we were to be tested for infertility and then there being a possibility of being on a 2 year IVF waiting list, I made the decision to leave my old employment and try to get a less stressful job.
I figured it would be years before we actually fell pregnant anyway (since I'd convinced myself that IVF was the only solution)
Then low and behold, as the IVF referral letter arrived, we found out we'd managed to conceive naturally (was deffo stress related now looking back)
I think after explaining all of the above to him and making it clear that it wasn't my intention to start this job and get pregnant so soon - he should be ok
xx