Necrotizing enterocolitis, or NEC, is a serious intestinal disease that primarily affects premature babies. It occurs when tissue in the intestinal wall becomes inflamed and begins to die, sometimes leading to a hole in the intestine. NEC is the most common cause of death between 2 weeks and 2 months of age in extremely preterm infants, and about 7% of very low birth weight babies develop it.
How NEC Damages the Intestine
A premature baby’s gut lining is not fully developed. It’s more sensitive to bacteria than a full-term baby’s gut would be, and it’s also less effective at keeping bacteria where they belong, inside the intestinal space rather than crossing into surrounding tissue. When bacteria do cross that barrier, or when the immature immune system overreacts to normal gut bacteria, the result is intense inflammation that injures the intestinal wall.
That inflammation can progress quickly. The intestinal tissue swells, blood flow to the area decreases, and sections of the bowel begin to die. In severe cases, gas produced by bacteria accumulates in the intestinal wall and can even enter the veins leading to the liver. If the damage extends through the full thickness of the intestinal wall, a perforation (hole) develops, spilling intestinal contents into the abdominal cavity and causing a life-threatening infection.
Which Babies Are Most at Risk
Any baby born before 37 weeks or weighing less than about 5.5 pounds at birth has an increased risk of NEC. The smaller and more premature the baby, the greater the risk. About 7% of very low birth weight infants (those under roughly 3.3 pounds) develop the condition.
Though NEC is overwhelmingly a disease of preterm babies, it does occasionally affect full-term infants. One long-running study at a single children’s hospital found that about 9% of all NEC cases over a 30-year period occurred in babies born at term. These cases are rarer but can still be severe.
Signs and Symptoms
NEC typically develops in the first few weeks of life, often after a baby has started feeding. The earliest signs can be subtle and overlap with other common problems in premature infants, which makes it tricky to catch right away. Common symptoms include:
- Feeding intolerance: the baby can’t digest milk properly, with food remaining in the stomach longer than expected
- Abdominal swelling or bloating
- Stomach discoloration: the skin over the belly may turn bluish or reddish
- Pain when the abdomen is touched
- Bloody stools or changes in stool color and consistency
- Vomiting greenish-yellow liquid
- Lethargy: decreased activity or responsiveness
- Temperature instability: difficulty staying warm
- Episodes of slowed heart rate or pauses in breathing
In advanced cases, the baby’s blood pressure may drop and the pulse may weaken. Fluid can build up in the abdominal cavity, and infection may spread to the tissue lining the abdomen. If the intestine perforates, emergency surgery is needed. Pressure from the swollen abdomen can also make breathing significantly harder.
How NEC Is Classified
Doctors use a system called Modified Bell’s Staging to describe how far the disease has progressed, which guides treatment decisions. There are three main stages:
Stage I (Suspected NEC) involves nonspecific signs like temperature instability, lethargy, mild bloating, and traces of blood in the stool. Imaging of the abdomen may look normal or show only slight changes. At this point, the medical team monitors closely and begins precautionary treatment.
Stage II (Confirmed NEC) is split into mild and moderate illness. Bowel sounds may disappear, the abdomen becomes clearly tender, and imaging shows telltale signs like gas within the intestinal wall. In moderate cases, there may also be gas visible in the veins leading to the liver and fluid accumulating in the abdomen.
Stage III (Severe NEC) means the baby is critically ill. Blood pressure drops, breathing worsens, and there are signs of widespread infection. If the intestine has perforated, free air is visible on imaging. Stage III almost always requires surgery.
Treatment for Milder Cases
When NEC is caught early, treatment focuses on resting the gut and fighting infection. Feedings are stopped completely, and the baby receives nutrition through an IV instead. Antibiotics are started to control bacterial infection. The severity of the disease determines how long the baby stays off feeds and on antibiotics, with milder cases requiring shorter courses and more advanced disease requiring longer treatment. The medical team monitors with frequent blood work and abdominal imaging to track whether the condition is improving or worsening.
When Surgery Becomes Necessary
Up to 50% of babies with confirmed NEC eventually need surgery. The clearest reason is a perforation: when imaging shows free air in the abdominal cavity, it means the intestine has developed a hole. Other triggers include continued deterioration despite aggressive medical treatment, signs of an abdominal mass with intestinal obstruction, or a section of bowel that appears irreversibly damaged.
The most common surgical approach involves opening the abdomen, removing the dead or damaged sections of intestine, and creating a temporary ostomy, an opening that diverts the intestinal contents to a small bag on the skin surface. The ostomy is typically reversed in a later surgery once the baby has healed and grown. In some cases, the surgeon can reconnect the healthy ends of the intestine right away without an ostomy, though this depends on how much bowel is affected and how stable the baby is.
For the smallest and most fragile babies who may not tolerate a full operation, a less invasive option involves placing a drain in the abdomen to release infected fluid and relieve pressure. This can stabilize a critically ill baby enough to undergo a more definitive surgery later, and in some cases it serves as the only procedure needed.
The Role of Breast Milk in Prevention
Breast milk is the single most effective tool for reducing NEC risk. Extremely preterm infants who received more than about 50 milliliters per kilogram per day of their mother’s own milk had a 50% lower rate of NEC compared to babies fed formula or a mix of breast milk and formula. Even more striking, babies whose diet was more than half breast milk during the first 14 days of life had an 83% reduction in their chances of developing NEC afterward.
The protective effect scales with the amount of breast milk a baby receives. For every 10% increase in milk intake from a source other than the mother’s own milk, the risk of NEC rose by 21%. This is why neonatal intensive care units strongly encourage pumping and breast milk feeding for premature infants, even when babies are too small to nurse directly.
Long-Term Effects for Survivors
Babies who survive NEC, particularly those who needed surgery, can face lasting health challenges. Short bowel syndrome is one of the most significant: when large sections of intestine are removed, the remaining gut may not absorb enough nutrients, leading to prolonged dependence on IV nutrition and ongoing issues with growth and malnutrition. Intestinal strictures (narrowed areas caused by scar tissue) can develop weeks to months after the initial episode, sometimes requiring additional surgery.
NEC survivors also face a higher risk of neurodevelopmental delays. The reasons are likely layered. The illness itself causes severe inflammation and stress during a critical window of brain development. On top of that, babies with NEC often experience complications like infections, nutritional deficits, and prolonged hospitalization, all of which can independently affect brain growth. These children may need developmental follow-up well beyond infancy to identify and address any emerging learning, motor, or cognitive difficulties.