Blabbing parents and job worries

I'd love any advice or experience on when to tell family. My parents are notorious for not keeping secrets. They have posted my siblings past pregnancies/births on Facebook before my siblings could!! To add to the challenge they know that we did an iui this month and should know the results soon. We are almost 5 wks prego but I really don't want to tell them yet but I also don't like lying. Part of the concern is my job. I teach at a university and they are not super supportive of taking time off. Do not have paid leave and I will have baby midsemester in March. I want to wait until at least 2nd trimester to tell my job - prob October sometime. If I wasn't worried about my jobs reactions I'd have no worries about it leaking on Facebook. Any suggestions??!