What is the most reliable indicator of viability in a premature infant?

The Apgar score is the most reliable indicator of viability in a premature infant. The Apgar score is a quick test that is given to all newborns at 1 minute and 5 minutes after birth. The score is based on five criteria: heart rate, respiratory effort, muscle tone, reflex response, and color. Each criterion is given a score of 0, 1, or 2, for a total possible score of 10. A score of 7 or higher is considered normal, while a score of 4 or below is considered critical. The Apgar score can help to determine whether a premature infant needs immediate medical attention.