When did you start maternity leave?

I get 6 months of for maternity leave where I work. (Lucky I know) Im 38 weeks now and hoping my dr will let me start maternity leave a few days before my due date. I work rotating 12s and the week of my due date I will be working nights. Ughhhh..... Can I request to start my leave early? Assuming I don’t have my baby by then. Has anyone did this? I’m new to it all and don’t know how it works.