This study is designed to evaluate a novel tool to aid in the diagnosis of intestinal perforation in infants who are at high risk. Analysis of perforation rates of all infants in the three largest participating sites shows that the majority of infants with perforation will do so prior to day of life 21. This study will target the group of infants at highest risk for IP, those with birth weight less than 1000 grams, within the time frame most likely to capture the perforation. Hypothesis: An IRT value exists that can adequately differentiate premature infants with and without intestinal perforation in the first 3 weeks of life.