I found out I was pregnant right after I took a new job. By right after I mean my first day. With DD I wasn't working so I didn't have this issue. I just feel like I am new and I don't know these people well so I don't really know how to tell them. I still have a few weeks before even thinking about telling them but it is something I keep thinking about. I am a bit of an introvert so I'm very good with these things.
Re: Telling coworkers
I've been at my job for almost 7yrs and I am nervous about telling, so I understand!
I'd wait until you're out of the first trimester, like 12/13wks. And from there I'd tell your boss first. When you talk to your boss be prepared to discuss your plans for after baby is born, like whether you plan to return. I would also look in to what kind of leave options you have, since you won't have been there 12m you aren't protected by FMLA but many places will work with you.
I found simple/straight to the point is easiest, so I wanted to let you know, I'm having a baby in x month.
Good luck!
I agree with PP - come in with a game plan and keep the conversation focused on practical matters. Don't dwell on how this is awkward or kind of embarrassing to bring up. At most, you could acknowledge it's a pleasant surprise, but I definitely wouldn't go beyond that.
Set up an appointment with your boss, say you have some news to share - you're expecting, due on such & such date, and wanted to give as much heads up as possible. You'd like to be take X weeks of leave and will work with your boss to make sure whatever loose ends are tied up before your leave and that you've trained whomever s/he assigns to cover the basic tasks while you're out.
I've been at my job forever and didn't want to tell people.. My boss new pretty early (not drinking at a conference in Vegas kind of drew suspicion), but I didn't make any announcements until I was well past 20 weeks..(I was tiny. Not so tiny anymore!)
I think you really only need to tell your immediate co-workers when you'r ready, and everyone else can find out later.