| Stage | Systemic | Abdominal | Radiologic |
| I (suspected NEC) | A&Bs, lethargy, temp. instability | residuals, guiac positive stools | normal, or nonspecific |
| IIA Mild | As per I | distention, tenderness, absent bowel sounds, blood in stool | ileus, dilated loops, focal pneumatosis |
| IIB Moderate | Mild acidosis | Abdominal wall edema, tenderness, with or without masses | Extensive pneumatosis, early ascites, possible intrahepatic portal venous gas |
| IIIA Advanced | Respiratory and metabolic acidosis, assisted ventilation, decreased urine output, decreased BP | Increased edema, abdominal wall erythema, induration of the abdomen | Ascites, sentinel loops, no perforation |
| IIIB Advanced | Deteriorating general condition, vital signs, electrolyte disturbances, shock | Perforation | Perforation |