Hi : We do car seat tests on any infant under 37 weeks or if they have poor muscle tone. The test is 1 hr long and they are on the montior with a pulse ox. If they fail the test as demonstrated by A's and B's we repeat the test the next day, we have a sheet to record their V.S every 15 mins.We do use rolls if necessary. If they fail, they need to go home in a car bed and be followed by their Dr. Donna