Meconium Aspiration Syndrome

Meconium Aspiration Syndrome InfographicMeconium aspiration syndrome (MAS) is a potentially dangerous medical event during childbirth that occurs when a baby inhales meconium and amniotic fluid during childbirth.

Meconium is essentially a baby's first poop. It is a thick, dark-green, viscous fecal substance that babies excrete during the first few days after birth. Sometimes towards the end of a pregnancy, the baby will excrete meconium inside the womb where it mixes with the amniotic fluid. MAS occurs when meconium is discharged inside the womb. The baby inhales it into her lungs before birth. MAS can cause serious health risks and complications for a baby. If not properly treated, the child can suffer permanent injury or death.  

What Causes MAS?

MAS occurs when a baby discharges meconium inside the womb and then inhales it. Normally a baby does not discharge meconium until after they are born. The question of what causes MAS is an issue of what cause meconium discharge inside the womb. Early discharge of meconium inside the womb is often triggered by fetal stress or abnormalities involving the placenta. Fetal distress in the later stages of pregnancy is almost always related to some type of oxygen deprivation or oxygen reduction to the fetus. Common causes of fetal distress and/or oxygen interruption leading to MAS include:

  • Post-term pregnancy (anything past 40 weeks)
  • Prolonged or traumatic labor
  • Maternal health issues such as preeclampsia or gestational diabetes
  • Maternal infection

Post-term pregnancy probably has the strongest link with increased risk of MAS. Babies do not begin to produce meconium until the last stages of pregnancy. The longer a pregnancy goes past the due date the more likely it is that a baby will discharge meconium in the womb. Moreover, as the pregnancy progresses past the due date the amniotic fluid level decreases. This makes any meconium discharge more concentrated.

Symptoms of MAS

The most noticeable initial symptom of MAS is respiratory distress after birth. Newborns with MAS will often exhibit rapid or abnormal sounding breathing. If too much meconium is inhaled, it can block the baby's airways and can prevent breathing. Additional symptoms commonly associated with MAS include:

  • Cyanosis (blue or purple skin color)
  • Low muscle tone or limpness
  • Low blood pressure
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Diagnosing MAS

MAS is almost always something that is immediately diagnosed by the doctors and/or nurses in the labor and delivery room after birth. When meconium is discharged inside the womb, it usually stains the amniotic fluid. Meconium staining is usually easy to spot and often the first warning sign of MAS. If the amniotic fluid is stained by meconium doctors will usually carefully assess the baby for additional signs of MAS. This is usually done just by listening to their chest but x-rays are also an option.

For reasons that are not fully understood, African-American newborns suffer from meconium aspiration syndrome 50% more often than white newborns. 

Treatment of MAS

Babies with MAS require immediate intervention and treatment. Treatment for MAS usually begins with manual removal of any meconium and amniotic fluid from the baby's airways. At first, the doctor will probably clear any fluid by hand and then additional fluid will be cleared with a suction tube. The suction tub gently dislodges any meconium-stained fluid and sucks it out of the airways.

After initial suction removal is complete the baby's respiratory functioning will be reassessed. If the baby is still having difficulty breathing the next treatment step typically involves a bag/mask ventilation device to facilitate oxygen delivery to the baby. The manual delivery of oxygen with the ventilator helps get oxygen to the baby's organs.  This also also helps to inflate their lungs and get any meconium and fluid out.

If the baby is still having trouble breathing after suction and ventilation are applied, then the next level of treatment for MAS involves the surgical insertion of a breathing tube. A breathing tube is inserted into the baby's windpipe and attached to some type of mechanical ventilation machine. Babies who require this level of intervention will be placed in the NICU unit.

After the emergency intervention treatments are administered, babies with MAS will often receive follow up monitoring and treatment to avoid potential complications. Common follow up care for MAS includes:

  • Oxygen therapy
  • Placing the baby under a radiant warmer to maintain body temp
  • Antibiotics to guard against infections associated with MAS
  • Mechanical breathing devices (if necessary)

In some of the more extreme cases of MAS, where the baby is not able to breathe independently or has very high blood pressure in their lungs, extracorporeal membrane oxygenation (ECMO) may be necessary. With ECMO the baby is hooked up to a complex breathing machine that will essentially perform the function of the lungs and heart.

Potential Complications From MAS

MAS can usually be effectively managed and treated without any long term health complications or injuries. Approximately 10%-15% of pregnancies are complicated by meconium-stained amniotic fluid. Only .2% (2 out of 1000) of these infants will develop MAS.

But the risks are still grave if MAS is not properly treated.  Typically, the problems with MAS are respiratory and MAS is a major cause of serious respiratory disease.   Meconium discharge often triggers inflammation and infection in the lungs. Infection is probably the most common complication associated with MAS.

Another potential complication is the over-expansion of the lungs. When airways are obstructed by MAS the air pockets in the lungs often over-expand to get more oxygen. If the lungs over-expand or inflate too much in response to MAS they can potentially rupture and even collapse. If the lung rupture the air can escape into the chest cavity (a condition called pneumothorax) which makes it very hard to inflate and repair the lung. Lung rupture or collapse is probably the most dangerous complication associated with MAS.

MAS also increases a baby's risk of developing a condition called persistent pulmonary hypertension of the newborn (PPHN). PPHN is a very rare but potentially life-threatening condition in which high pressure in the blood vessels surrounding the lungs restrict circulation making it very difficult for the baby to breathe.

Meconium Aspiration Medical Literature
  • Buzdar N:Factors Leading to Meconium Aspiration Syndrome in Neonates. Journal of Rawalpindi Medical College. 2017 Dec 30;21(4):371-5.
  • Dargaville PA, Copnell B:  The epidemiology of meconium aspiration syndrome: Incidence, risk factors, therapies, and outcome. Pediatrics 2006; 117:1712-21.
  • Walsh MC, Fanaroff JM:  Meconium stained fluid: Approach to the mother and the baby. ClinPerinatol. 2007; 34(4):653-65.
  • Frey HA, et. al: Interpreting category II fetal heart rate tracings: does meconium matter?. Am J Obstet Gynecol. 2014; 211(6):644.e1-8.