Yack, planning ahead is great!
First off, you should be able to get a copy of your companies policies from human resources that should explain the FMLA (Family Medical Leave Act). That is normally unpaid leave. For maternity leave, if you have any vacation/sick/personal time available, you should be able to use that time up while on leave.
I hope you find the answers to your questions easily! Good luck with the planning

sabby