New Job and Pregnant

I'm currently 9w and I just got a new job. My official first day will be Mar 9th. When do I tell my manager? I haven't even told family and friends yet. I wanted to wait until 12w or later before a public announcement. I've been reading articles from Forbes and Business Week and other places, and there are so many opinions!! Some say after the first few interviews, at the time of the job offer, when I start to show, or even 60 days prior to departure for mat leave. I'm confused. I've never been in this situation before. I couldn't afford to NOT work. I just relocated out of state and I had to find a job. So now I've got the job, but what to do about my pregnancy??