I'm a news reporter and was scared to tell work because I didn't want to lose my beat, etc. I gave in and told my editor at 13 weeks. He was very supportive and excited for me, and didn't mention changing beats. I understand the worry though...I was really nervous. But all was well. I felt a lot better once I took the plunge and told people! And now if I get sick or have a doctor's appointment, he understands why and there's no questions.
Good luck!!
I already told my job since it entails lifting and spotting children. I think it is your business and unless there is no danger to you or your child, tell them when you think it is appropriate. When you start to show, it will be obvious. It may hurt some feelings if you wait until they figure it out. I don't know what kind of work environment you have. It seems like they would be supportive so I would tell them all together. good luck