How do you keep a secret....

We kept the pregnancy a secret for as long as we thought wise, the customary 12 weeks, I am desperatly trying to hide it from work (my boss knows) for as long as possible, I am really hoping I can make it to Christmas, it is not that I am not totally happy about the pregnancy, but I do not want my work persona to be violently shifted from competent professional to pregnant lady. That and I enjoy keeping secrets and avoiding horrific labour stories for as long as possible.