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.

At least 300 infants age 1-16 days will be enrolled. IRT values will be obtained daily through day of life 21, if the infant is already having labs drawn that day. The primary outcomes will be intestinal perforation and/or death on or before day of life 21. Each patient will be followed until death or discharge. Discharge will be defined as the release of the infant to home. Infants who are transferred to another NICU may be followed if the receiving NICU is one of the investigational sites. Transfer includes the release of the infant to outside units or other units within the same hospital. The purpose of this follow up is to obtain serial IRT values through day of life 21.

Inclusion Criteria:

• Informed consent
• Birth weight less than 1000 grams
• Admitted to investigative site within first 16 days of life.

Exclusion Criteria:

• Evidence of Intestinal perforation in utero
• Suspected or confirmed custic fibrosis
• Abdominal wall defect or intestinal atresia
• Concomitant medical condition that may create an unacceptable risk.

Premature infants less than 1000 grams, age 1-16 days