Maternity leave question-ohio

I am a teacher and I am due April 26,2020. I would like to start my maternity leave before I have the baby. I would like to start around March 9th which is less than 12weeks before school is out so I won’t be taking a full 12weeks. But I would like to start it before I have the baby. If I have it and save up I might as well use it.

How does this work? Do I need to have doctors note or can I tell HR I plan to start maternity leave March 9th-end of year? That way they can find coverage.

During that time I will remodel and have baby shower etc. plus I’m High risk.