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Meconium Aspiration Syndrome

Meconium aspiration syndrome (MAS) is a condition that occurs when a newborn infant aspirates (or breathes in) a mixture of meconium and amniotic fluid (the fluid in which the baby floats inside the mother). Meconium is a newborn infant's first bowel movement, which is sticky, thick and dark green and is typically passed the first few days after birth. For reasons that are not always well understood, the baby will sometimes pass this first bowel movement while the infant is still in the womb. During the birth process the yet-to-be-born baby may breathe in or aspirate this meconium. This aspiration can happen hours before, during or immediately after delivery.

The aspirated meconium can partially or completely block the baby's airways, making it difficult for the infant to breathe and causing irritation or a lung infection. Further, meconium prevents the normal function of an important lung chemical called surfactant, which helps the lungs expand properly. The result of these meconium aspiration effects is a baby with mild, moderate to severe difficulty breathing.

How severe the problem becomes depends primarily on the amount of meconium the baby aspirates, how long before delivery the meconium was aspirated and how soon the problem is discovered and treated.

The likelihood of an infant passing meconium before birth increases as the infant nears his or her due date and markedly increases after the due date. Although meconium in the amniotic fluid is not rare, occurring in 8–15% of babies delivered at or near term, the vast majority of infants who pass meconium during labor and delivery do not get MAS.


Many believe that MAS is related to some stress during the labor and delivery process.

Some examples of conditions that may lead the infant to become stressed before birth include:

  • A mother who is a heavy cigarette smoker or who has diabetes, high blood pressure or other medical condition
  • Poor growth of the baby while in the womb
  • A prolonged or difficult delivery
  • An infant who is significantly past his due date
  • Complications with the umbilical cord or placenta
  • Infection

Note: MAS is very rare in babies born before 34 weeks.

Diagnosis & Treatment

If the doctor believes the baby has aspirated meconium, treatment will begin during delivery. After the baby's head is delivered, the physician will suction the baby's mouth and nose to clear any meconium present.

Immediately after birth, the doctor will evaluate the baby's activity and breathing. If the baby is limp or slow to begin breathing, the doctor may then insert a tube into the baby's trachea to remove any meconium that might be present before stimulating the child to breathe.

If the baby shows signs of breathing problems the doctor or a neonatologist, a pediatrician trained in the care of sick newborns, will continue to support the infant and admit the baby to a special care or Neonatal Intensive Care Unit (NICU). In the NICU, careful examinations and laboratory tests such as chest x-rays and blood tests will help determine the presence of MAS. 


  • Evidence of meconium (dark green streaks) in the amniotic fluid and on the baby's skin
  • Breathing problems such as rapid breathing, labored breathing or periods of not breathing immediately after birth
  • The baby's lips and mouth may be bluish (low blood oxygen)
  • Limpness in the infant at birth or low Apgar scores (a system to evaluate the condition of the newborn immediately after birth) 


If the baby is suspected of meconium aspiration but generally appears well, the health care team may simply observe the baby for symptoms such as increased respiratory rate, grunting or cyanosis.

However, if an infant has aspirated meconium and appears ill, the first priority is to ensure the baby is well oxygenated by supplying extra oxygen and supporting his breathing. Further treatments may include:

  • Breathing support through nasal cannula or mechanical ventilation
  • Fluid and nutrition through an intravenous catheter (IV)
  • IV antibiotics
  • Obtaining blood routinely to assess the baby's oxygenation and ventilation

Alternative Treatment

If the above therapies (or a combination of them) do not work, there is another alternative. Extra corporeal membrane oxygenation (ECMO) is a form of cardiopulmonary bypass, in which an artificial heart and lung machine temporarily takes over to supply blood to the baby's body.

Babies who have severe aspiration and require mechanical ventilation are at increased risk for the following conditions:

  • Pneumothorax–a collapsed lung, treated by inserting a tube into the collapsed lung, allowing the lung to gradually re-expand
  • Aspiration pneumonia–an infectious complication is treated with antibiotics
  • Bronchopulmonary dysplasia–a chronic lung condition be treated with medication or oxygen
  • Pulmonary hypertension (PHN)

In severe cases, MAS may lead the infant to revert to the blood circulation pattern found in the womb. This pattern of blood flow bypasses the lungs, which makes newborn infant's blood be severely low in oxygen. This condition may be treated with a several medical interventions including a medical gas called nitric oxide (NO). Nitric oxide is a medicine that is breathed in, causing the lung blood vessels to dilate, which allows more blood to reach the lungs and raise the level of oxygen in the baby's blood.

Long-Term Effects

Most babies with uncomplicated MAS improve within a few days or weeks, depending on the severity of the aspiration. Although a baby's rapid breathing may continue for days after birth, usually there is no severe permanent lung damage. Some studies, however, suggest that those born with MAS are at a higher risk of having more sensitive lungs, which may lead to an asthmatic-like condition.

Severely affected babies have a much more guarded prognosis; they may develop chronic lung disease, developmental abnormalities and hearing loss. Sometimes very severe cases of MAS can be fatal. Studies suggest that deaths from MAS have decreased significantly through prompt and thorough suctioning and reducing the number of births that go beyond 40 weeks.