This is my 3rd baby in less than 3 years, and I’m scared to tell my work… Suggestions or advice are SO appreciated

I am currently 12 weeks pregnant with baby #3, and am excited to announce publicly to all family and friends (immediate knows), but I can’t post on my FB until I tell my job… and I’m so nervous because this is my 3rd baby in under 3 years, all of which have happened at the same company. I have a 2 year old and a 7 month old already, and I have a very demanding corporate job. Idk but I feel like they are going to “be supportive”, but it’s going to be with that thought in the back of their mind that this will be my third extended leave (maternity leave) in less than 3 years… Little do they know I will be quitting in a few months anyways to be a stay at home mom, but I don’t want them knowing or thinking that until 2 weeks before because I want to make sure they don’t try to switch me to a lesser role because they know/suspect I’m leaving. I know legally they can’t do that…. And I’ve technically been with the company 5 years and am very respected, but legal or not, you ladies in the corporate world know how they always use their smooth talking and find loopholes anyway they can to benefit themselves… Which is why I am waiting and only giving a standard 2 weeks. But I’m so scared to tell them I’m pregnant at all, which they need to know because of frequent appointments, and would love advice on how to approach. Thanks in advance ladies 🥰