Just found out i am pregnant last thursday and i'm absolutely over the moon.
I told my employer after the 12th week scan. Wanted to make sure that everything is ok too. Most women in the UK, however, dont tell their employer much before the 20th week...
I'd say try to see how you get on with your shifts, combining with the tiredness (&maybe pregnancy sickness) which will come in the next few weeks. When you notice you can't handle it anymore talk to your employer then.
I think that most people tell their employer when they get to the 12 week mark. If you're finding the 12 hour shifts difficult, then it would definitely be worth saying something sooner - more important to mind yourself and babs and so what if a few people find out!
belle1, as you work shift work, I'd discuss this with your GP (as it probably too early to discuss yet with the hospital consultant). That way, if you are in a low-risk category, no need to tell work till 12 weeks at least, if you managing ok.
But shift work is tough very tough when you are pregnant and the extra reassurance and advice from someone medical will help.
Congrats on your pregancy
If you're comfortable telling your boss and trust them to keep it to themselves then I would tell them sooner rather than later. I work in a pretty physical job with long hours and wasn't going to tell anyone until 12 weeks but told 1 person that I work alongside at about 7-8 weeks and it made things far easier for her to know what was going on with me and take some of the physical burden off me when she could.
I would say it to your boss in confidence but tell them you want to continue as normal for as long as possible, but if things are getting too much for you then at least they would be in the know and possibly already preparing for changes.