I don't know if it works the same everywhere, but we didn't actually pick out our pediatrican until the day our DS was born. They asked us which ped we wanted, we told them and when that ped came to do rounds that morning we met him for the 1st time. With DD we had told the ped while I was pregnant, but nothing official with the office. When she was born we just listed him again. Unfortunately our ped just switched offices because he partially retired, so we decided to go with someone new this time (incase he decides to fully retire soon)...so I'm hoping it all goes as well as the last 2 time!