What is Congenital Diaphragmatic Hernia?

Congenital Diaphragmatic Hernia (CDH) is a life-threatening condition caused by a baby’s diaphragm not forming properly during pregnancy. The diaphragm is the main muscle that helps us breathe, and also separates the chest cavity from the abdominal cavity. The hernia (or hole) can occur on either the left or the right side of the diaphragm, or very rarely, can be on both sides (bilateral). In most cases (about 80%) the hernia is on the left side.

Because of the hole in the diaphragm, abdominal organs such as the stomach, intestine, liver and spleen, can move through the hole into the chest cavity where the lungs and heart are. This means the lungs have insufficient space to grow normally and are therefore smaller than they should be. A smaller lung size can also mean that the lungs cannot grow as many air sacs (alveoli). Babies with CDH are usually born with less lung sacs and tissue than a baby that does not have this condition. The lung on the side of the hole is always the smallest lung. The lung on the other side is also usually smaller than normal because the heart is pushed across and restricts growth. For example, if a baby’s hernia is on the left side, the left lung will be much smaller, but this may in turn push the heart to the right, therefore affecting the right lung’s growth as well.

Because lungs have blood vessels, these blood vessels can be narrowed or damaged when squashed, which can then slow the blood flow in the lungs, which in turn increases blood pressure in the lung arteries. This means the heart must work harder to pump blood through the lungs, which can weaken the heart muscle due to the extra exertion. This is known as Pulmonary Hypertension. Therefore, when a baby is diagnosed with CDH, there are concerns around the lungs and the heart, with both requiring monitoring.

CDH is usually an isolated structural condition, although other congenital anomalies, most commonly cardiac, may be associated and influence the prognosis. Sometimes CDH is also linked to a genetic cause, which will affect the prognosis and could mean the baby is affected by other physical and developmental issues.  An obstetrician may recommend genetic tests for babies diagnosed with CDH before birth, or might refer parents with a CDH baby to see a geneticist.

Currently, the survival rate for babies diagnosed before birth with CDH in Australia is 50%. Due to advances in intensive care treatments in the last 15 years, about 70–80% of all babies who get admitted to a Neonatal Intensive Care Unit (NICU) with CDH will survive.

The main determinants of survival include the degree of underdevelopment/undergrowth of the lung and the supplying blood vessels, with associated pulmonary hypertension, any other genetic or congenital problems, as well as the gestation of the baby at diagnosis and at birth.

CDH can be detected during pregnancy from ultrasound scans (at various stages of pregnancy). Some cases of CDH are not detected during pregnancy and are only realised after birth when a baby has difficulty breathing. And, in rare cases, CDH is not diagnosed until well after birth (these cases are rare and usually due to a very mild hernia).

There is no known cause for CDH, nor is there currently any cure or prevention for this condition. CDH is a condition that once diagnosed, is mainly treated through post-birth care which includes a baby being put on a breathing machine and requiring surgery. There is some research being conducted into in-utero surgery for babies. In Australia in-utero surgery is only being offered to babies with the most severe lung underdevelopment.

Useful resources

Download: What is CDH?

Download: Expecting a baby with CDH booklet

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