Reason for The Police
The doctor knew that parents, especially mothers, cannot stay calm in a situation like this. Often, they will start making trouble. These troubles will cost time and the doctor didn’t have enough time to help her baby and calm Susan down. This is part of the reason why he called the police.
Another reason lies in the main explanation you can see below. It is mandatory to call the police when things like this happen. Susan thought that she was responsible for all that happened to her baby. Was she responsible for this?