HomeHealth A-ZMeconium Aspiration Syndrome (MAS): Causes, Symptoms, and Treatment

Meconium Aspiration Syndrome (MAS): Causes, Symptoms, and Treatment

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Meconium is the first stool the newborn baby passes. Meconium aspiration syndrome (MAS) occurs if the newborn swallows a combination of meconium and amniotic fluid into the lungs before labour. It is a leading cause of severe illness and death in newborns and occurs in around 5 to 10 per cent of births. The condition usually occurs if the fetus is stressed during labour, mainly when the pregnancy is past its due date. 

This blog explains the meconium aspiration syndrome (MAS), its symptoms, causes, complications, treatment and prevention in detail.

What is MAS?

The fetal intestines produce a dark green faecal material known as meconium before birth. The newborn baby passes meconium stools initially for some days after delivery. However, the baby can pass meconium stool due to  stress they experience before or during birth when they are still in the uterus. 

This causes the meconium stool to mix with the amniotic fluid surrounding the fetus. The baby can breathe the mixture into their lungs shortly before, during, or immediately after birth. It is called meconium aspiration or meconium aspiration syndrome (MAS).

This may lead to severe health complications for newborn babies and can be fatal if severe or left untreated. 

What are the symptoms of MAS?

The most significant symptom of MAS is respiratory distress. The newborn baby can breathe rapidly or grunt when they breathe. Some of them can stop breathing if meconium obstructs their airways. The baby can also display symptoms, including low blood pressure, limpness and bluish skin colour (cyanosis).

What are the causes of MAS?

MAS can occur if the baby experiences stress in the womb. Generally, when the fetus receives less oxygen, it causes stress to the baby. Babies may also probably pass meconium because of the following factors:

  • Difficult or long labour
  • A pregnancy extends past the due date
  • Women suffer from health problems, such as diabetes or high blood pressure.
  • Women smoked or used drugs during pregnancy
  • Babies did not grow well before birth

Babies can also pass meconium before birth when stressed by low oxygen levels or infections.

What are the complications of MAS?

MAS does not cause any long-term health complications in most newborn babies if addressed on time . However, MAS can immediately seriously impact the newborn baby’s health. Meconium in the lungs may lead to inflammation and infection and obstruct the airways, resulting in over-expansion of the lungs. A lung may rupture or collapse if it inflates a lot or expands. The air from the inner lung can then collect in the chest cavity. The condition known as pneumothorax .

MAS also elevates the newborn baby’s risk of developing a condition known as persistent pulmonary hypertension of the newborn (PPHN), a rare, life-threatening condition. High blood pressure in the lungs vessels obstructs the blood flow and makes breathing challenging for the newborn baby. Severe MAS can also  restrict oxygen to the brain, leading to permanent brain damage.

How is MAS treated?

The newborn baby requires treatment immediately to remove the meconium from the upper airway. After labour, the doctor instantly suctions the nose, mouth, and throat.

The doctor could insert a tube into the newborn baby’s windpipe (trachea) to draw the fluid containing meconium from the windpipe when the baby is not breathing or does not respond well to the initial treatment. The doctor can continue the suctioning till they do not see the meconium in the material removed.

The doctor uses a bag and a mask to assist the newborn baby in breathing if they continue to breathe laboriously or have a low heart rate after suctioning. The bag and the mask supply oxygen to the baby and inflate their lungs.

The doctor may place the newborn baby in a special care unit to observe the newborn baby’s breathing after they receive emergency treatment. Doctors can provide further treatment so that a newborn baby does not suffer MAS complications. The common treatments include the following:

  • Oxygen therapy to ensure there is sufficient oxygen in the blood
  • Use of a radiant warmer to assist the baby in maintaining body temperature
  • Antibiotics, such as ampicillin and gentamicin, treat or prevent an infection
  • Use of a ventilator to aid the baby in breathing.
  • Extracorporeal membrane oxygenation (ECMO) is used if the baby does not respond to other treatments or suffers from high blood pressure in the lungs (in this treatment, the doctor uses a pump and machine to perform the newborn baby’s heart and lung functions so that the organs heal)

How can doctors prevent MAS?

The best way to prevent MAS is early detection. The doctor can decide if the baby is experiencing stress through fetal monitoring before delivery. They may take steps to ease fetal distress during labour and lower the baby’s risk of developing MAS. When the baby experiences stress, the doctor is prepared to evaluate and treat the baby immediately if they display MAS symptoms.


Newborn babies experiencing mild complications of MAS typically have a good recovery. If MAS causes brain damage or PPHN, newborn babies can face lifelong health issues where medical support is necessary.

Frequently Asked Questions (FAQs)

1. How is MAS diagnosed?

Doctors make a diagnosis depending on the newborn baby’s symptoms and the amount of meconium in the amniotic fluid. The doctor listens to the newborn baby’s chest through a stethoscope to detect abnormal breathing sounds. They can also use other methods to confirm the diagnosis, including:

  • Blood gas test to assess the oxygen and carbon dioxide levels
  • Chest X-ray to check if the material has entered the newborn baby’s lungs

2. Do newborn babies recover fully?

Most newborn babies with this condition make a full recovery. Some of them can be at a greater risk of lung infections and wheezing, especially in the first year of their life.

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