Need a little advice..

So, I am currently 11 weeks pregnant. At the beginning of the year I had applied and interviewed for a job that I had wanted so bad, they told me that the department I applied for was having a government freeze, and they would get back to me. Well fast forward to 3 weeks ago when I got a call saying that the freeze was off and they wanted to offer me the job. I immediately accepted it and was so excited. I was 8 weeks pregnant at the time. We dont tell anyone until around 14 weeks due to previous loss. So I need advice on how to tell my new job that I'm pregnant. I start in 2 weeks and I will be 13 weeks when I start. This Is my second baby, I have a 19 month old as well, so I'm showing soooooo much sooner than I did with my son. I'm so nervous that when I tell them they will find a way to have me not pass my probation.. or they will be upset I didn't let them know when they called with a job offer. Thanks in advance!!