CDH, or congenital diaphragmatic hernia, is a birth defect where a hole in the diaphragm allows abdominal organs to push up into the chest cavity, crowding the lungs and preventing them from developing fully. It affects roughly 1 in every 3,600 live births worldwide. The condition ranges from mild to life-threatening, and treatment typically involves intensive neonatal care followed by surgical repair.
How CDH Affects the Body
The diaphragm is the dome-shaped muscle separating the chest from the abdomen. In a baby with CDH, a gap in that muscle forms during early fetal development, usually between weeks 8 and 10 of pregnancy. Organs like the stomach, intestines, spleen, or even part of the liver can slide upward through the opening into the chest.
The most important consequence is underdeveloped lungs, a condition called pulmonary hypoplasia. For years, doctors assumed the lungs were small purely because abdominal organs were physically compressing them. Research now shows that the picture is more complicated: some degree of lung underdevelopment happens independently, as an intrinsic problem with how the lungs grow, not just a result of crowding. This distinction matters because it helps explain why some babies with relatively small hernias still have significant breathing problems.
The underdeveloped lungs also tend to have abnormal blood vessels, which can cause dangerously high blood pressure in the arteries feeding the lungs. This pulmonary hypertension is one of the biggest threats to a newborn with CDH, because it forces the heart to work against extreme resistance to deliver oxygen to the body.
Types of CDH
The two main types are named after the anatomists who described them. Bochdalek hernias, by far the most common, occur at the back and side of the diaphragm. About 80% of Bochdalek hernias appear on the left side, though they occasionally occur on the right or on both sides. Morgagni hernias account for only about 3% of cases and involve a defect at the front of the diaphragm near the breastbone. Morgagni hernias tend to be smaller and less severe, and some aren’t even discovered until later in childhood or adulthood.
The size of the defect varies enormously. Some babies have a small opening with a thin membrane partially covering it, while others are missing a large section of the diaphragm entirely. This range in severity is one reason outcomes differ so much from one baby to the next.
Causes and Genetic Factors
In about 70% of cases, including most babies who have CDH with no other birth defects, doctors cannot identify a specific genetic cause. In the remaining 30%, genetic differences play a clear role. These include chromosomal abnormalities (such as extra or missing chromosomes), deletions or duplications of small DNA segments, and changes in individual genes. CDH can also appear as part of broader genetic syndromes that affect multiple organ systems.
Most cases occur without any family history. There is no known way to prevent CDH, and it is not caused by anything a parent did or didn’t do during pregnancy.
How CDH Is Diagnosed Before Birth
Most cases are picked up on a routine prenatal ultrasound, often during the second trimester. The telltale signs include abdominal organs visible in the chest cavity and the heart pushed to one side. Once CDH is suspected, doctors measure the size of the baby’s visible lung tissue relative to head size to estimate how much lung has developed. This measurement, called the observed-to-expected lung-to-head ratio, compares the baby’s lung size against what’s normal for that gestational age.
Severity is graded based on that ratio and whether the liver has herniated up into the chest. A ratio below 25% with the liver up is considered severe. Ratios above 45% with the liver still in the abdomen are classified as mild. These numbers help medical teams plan delivery, assemble the right specialists, and counsel parents about what to expect. MRI can provide additional detail about lung volume and the position of herniated organs.
Prenatal Treatment for Severe Cases
For fetuses with severe CDH, a procedure called FETO (fetoscopic endoluminal tracheal occlusion) can improve outcomes. A tiny balloon is placed in the baby’s windpipe between 28 and 30 weeks of pregnancy through a small scope inserted into the uterus. The balloon traps fluid that the lungs naturally produce, and this trapped fluid acts like a gentle internal pressure that encourages lung tissue to grow. The balloon is removed after 4 to 6 weeks or at birth.
FETO is not offered to every family. It is reserved for babies with the most severe lung underdevelopment, specifically those with a lung-to-head ratio below 25% and the liver herniated into the chest. Clinical trials have shown survival benefits for severe CDH treated with FETO compared to standard postnatal care alone.
What Happens After Birth
Babies with CDH need immediate breathing support in the delivery room. Gentle ventilation is critical from the very first breaths, because aggressive ventilation can damage already fragile lungs. The medical team focuses on stabilizing the baby before any surgery takes place. This stabilization period can last anywhere from hours to days, and rushing to the operating room too early does not improve outcomes.
Babies who stabilize within the first 24 hours tend to have smoother recoveries with fewer complications. Those who take longer to stabilize face a more complex path, though the extra stabilization time itself does not increase mortality. It simply reflects a more severe case.
When pulmonary hypertension is severe and the baby cannot maintain adequate oxygen levels despite maximum support, a heart-lung bypass machine called ECMO may be needed. ECMO takes over the work of the lungs and heart temporarily, giving the baby’s body time to recover. The criteria for starting ECMO include oxygen levels that remain critically low, dangerous acid buildup in the blood, or blood pressure that doesn’t respond to medications.
Surgical Repair
Once the baby is stable, surgeons move the abdominal organs back down from the chest and close the hole in the diaphragm. Small defects can sometimes be stitched closed directly. Larger defects require a patch, typically made from synthetic material or biological tissue, to bridge the gap. Patch repairs are associated with a higher risk of the hernia recurring as the child grows, since the patch doesn’t stretch the way natural tissue does.
Surgery is performed through the abdomen or chest, and in some milder cases, minimally invasive techniques are an option. The length of hospitalization after repair varies widely. Some babies go home in a few weeks, while those with more severe cases may spend months in the intensive care unit.
Long-Term Health After CDH
Surviving the newborn period is a major milestone, but CDH often has lasting effects across several areas of health.
Lung and Heart Health
Pulmonary hypertension resolves in most babies over time, but 8% to 38% of survivors still have elevated pressures after leaving the hospital. These children need ongoing monitoring with heart ultrasounds. Lung function can remain reduced, and some children need supplemental oxygen or have exercise limitations that persist into childhood.
Feeding and Growth
Feeding difficulties are common. Many CDH survivors deal with severe reflux, inflammation of the esophagus, and oral aversion, meaning the baby resists feeding by mouth. Some require tube feeding for months or even years. Growth can fall behind, partly because of these feeding challenges and partly because the body’s metabolic demands are higher after critical illness. Persistent poor growth can in turn affect brain development.
Neurodevelopmental Challenges
CDH survivors have higher rates of learning disabilities, attention deficit hyperactivity disorder, and delays in motor skills, language, and cognition compared to their peers. The risk is greatest for babies who had larger defects, needed ECMO, required a patch repair, or spent extended time on oxygen. These effects can be subtle in early childhood and may not become apparent until school age, which is why long-term developmental follow-up is recommended for all CDH survivors.