Telling work

So I recently took a new job, like a week ago. The day I was offered the position & accepted it, I found out later that I was pregnant. I don’t know what to do or how to tell my new employer. I really don’t want to stay with the company I’m at because of it being in health care & interacting with sick people of all kinds & how high stress it is. But I don’t know how to tell my new job that I’m expecting. Should I tell them now? Or would it be best to wait till after my 12 week mark to let them know? I plan on working up till almost my due date, but I won’t even be there a year, I’m not sure I can take maternity leave. And what do I even say when I do tell them? I have health insurance through my husband so I don’t need & wasn’t planning on using any of their health benefits. All advice would be very helpful.