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.