Sharing the news with work...

Ladies, I could use some advise from working women. I currently work full time as a temp, however they are currently working on hiring me full time. I am currently 9 weeks pregnant with my first baby. I don't plan on working once the baby arrives, but I want to continue for as long as I can to save money. I don't want to be dishonest with my employer, but I also don't want to miss out on the opportunity by speaking too soon. I miscarried with my first pregancy so I don't feel comfortable sharing the news until I'm at least 12 weeks. I just feel like I'm in a tough situation because I don't want them to be mad when they find out after I've accepted the position. What would you do?