Congenital High Airway Obstruction Syndrome (CHAOS)

Congenital high airway obstruction syndrome (CHAOS) is a very rare condition where the fetal airway is fully or partly blocked. 

What is Congenital High Airway Obstruction Syndrome?

Congenital high airway obstruction syndrome (CHAOS) is a very rare condition where the fetal airway is fully or partly blocked. 

The blockage (obstruction) may be due to:

  • A larynx (voice box) malformation or blockage
  • A trachea (windpipe) malformation or blockage
  • A fluid-filled cyst in the larynx
  • Narrowing (stenosis) of the upper airway 
  • A web-like membrane blocking the larynx or trachea

CHAOS can be life-threatening if it is not treated. Advances in prenatal imaging, fetal interventions and postnatal care have improved outcomes.

What are the Signs and Symptoms of Congenital High Airway Obstruction Syndrome?

A normally developed fetus is always making fluid and releasing it through the mouth. A blockage in the fetal airway makes fluid go back into the lungs, trapping it. This makes the lungs get very large and puts pressure on the baby’s diaphragm and heart. The pressure makes it hard for the heart work and can lead to congestive heart failure. Fluid can also build up in the abdomen, trachea, bronchial tubes, and other areas. When fluid pools in the fetus’s body cavities and skin, it is called fetal hydrops.

What Causes Congenital High Airway Obstruction Syndrome?

The cause of CHAOS is not known. However, some cases may be connected to genetic or chromosome problems.

How is CHAOS Diagnosed?

CHAOS is usually found during a routine prenatal ultrasound. It may show these signs of the condition:

  • The lungs look large and bright.
  • The diaphragm is flattened or curved downward.
  • The heart looks flattened or longer.
  • You can see fluid buildup in the belly (abdomen) or other areas.
  • There is extra amniotic fluid because the esophagus is from compressed. 

If the doctor thinks your child has this condition these tests may be done:

  • Anatomy ultrasound – A high-resolution ultrasound to confirm the diagnosis, look at the airway and find other problems.
  • Fetal MRI – Non-invasive imaging to get clearer images of the airway, blockages and other conditions.
  • Fetal echocardiogram – A special ultrasound to look at the way the baby’s heart is made and works. 
  • Amniocentesis/chromosome studies – A medical procedure in which a small amount of amniotic fluid is taken and studied in the lab to screen for genetic problems.

After testing is done, specialists will look at your baby’s condition. They will recommend a plan of care, which may include fetal intervention.

How is CHAOS Treated During Pregnancy?

We will watch you and your baby closely during your pregnancy with regular ultrasounds. 

When considering fetal intervention, your medical team considers your baby’s gestational age, the location of the airway blockage and if there is an accumulation of fluid (hydrops) that could lead to heart failure. If hydrops occurs early in development, fetal surgery may be done to remove the blockage. For this surgery, a hollow needle is inserted into the mother’s abdomen and uterus and, eventually, the fetal airway. The needle will puncture the blockage and let fluid escape. 

In some cases, CHAOS resolves on its own. This is typically associated with obstructions related to a tracheal cyst or membrane.


Babies diagnosed with CHAOS are at high risk of having breathing problems at birth. Your doctor may recommend ex utero intrapartum treatment (EXIT). This is a special procedure done during a Cesarean (C) section. 

During this procedure, the surgeon delivers the baby’s head and upper part of the body while they are still attached to the placenta. The baby continues to get oxygen from the mother through the umbilical cord as the surgeon inserts a breathing tube into the baby’s mouth. If a tube cannot be placed, it may be inserted into the windpipe through an incision in the neck. This procedure makes sure the baby gets oxygen at birth and lowers the chance of damage to the brain or other organs. Once stable, the baby is fully delivered, and the umbilical cord is cut. The airway obstruction may be surgically repaired at the same time.

Babies with CHAOS must be delivered in a hospital that is ready to treat newborns with rare birth defects and mothers at high risk for complications. These babies need access to pediatric specialists, a neonatal intensive care unit (NICU) and pediatric surgical services. 

Treatment After Birth

Babies are closely watched in the NICU to assess the need for breathing assistance and other interventions. Some newborns may need a feeding tube and/or a heart-lung bypass machine to support their heart and lungs. It also is possible that additional surgeries will be performed to remove the blockage and reconstruct the airway.

Length of stay in the NICU depends on many factors, such as lung and heart function, the cause of the birth defect and any other surgical needs.

Long-term Effects

CHAOS is so rare that there is not a lot of information about the long-term health effects. However, improvements in testing, fetal surgery and postnatal care have helped develop better treatment and improve outcomes.

Potential problems, in the most severe cases, may include chronic problems with speaking, eating and drinking.