Marriage/baby delivery

My fiancé & I are getting married either September or October and our baby’s due date is November 10. It’s very important to me that we all have the same last name when he’s born. What do you have to show when getting admitted? Like can I show my marriage license or do I need to show my license/other form of ID. This is our first baby so I’m not sure what will be needed..I’m thinking October is cutting it too close to have my name changed