work leave question

is it possible to decide when you want to go on leave from work? even if a portion of it is unpaid until you actually give birth? I've read multiple things. nive read up to 11 weeks prior to due date, I've read 4 weeks prior to due date, I've read just whenever your company let's you? just wondering if any ladies had any ideas? (I'm in nj if that helps, I know some states have specific laws)