Meconium Aspiration Syndrome: Causes, Symptoms & Treatment

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Meconium aspiration syndrome (MAS) occurs when a fetus or newborn inhales a mixture of amniotic fluid and meconium into their lungs while still inside the mother’s womb or during labor.

Meconium is the baby’s first stool, which is a dark green, thick stool made of cells, mucus, and intestinal secretions. Usually, babies pass their first stool in the first few hours or days after birth. However, it may happen inside the womb in some cases during the late stages of pregnancy or labor (1) (2).

MAS may cause respiratory distress and lead to illness or other complications. Read this post to know more about MAS, inclusing its causes, diagnosis, related complications, and treatment.

Causes Of Meconium Aspiration Syndrome (MAS) 

A baby may expel meconium while still in the uterus due to decreased oxygen and blood supply (1) (3). It may also happen due to fetal distress caused by problems of the placenta or umbilical cord (4).

Below are some other risk factors that may cause fetal distress and premature release of meconium (1) (3).

  • Difficult delivery and prolonged labor
  • Aging of the placenta in cases of post-term pregnancy
  • Maternal conditions, such as diabetes, high blood pressure, cardiovascular disease, or chronic respiratory problems
  • Maternal substance use, such as smoking during pregnancy
  • Complications related to the umbilical cord
  • Poor fetal growth due to underlying problems or infections

Babies may usually have temporary breathing problems on inhalation of meconium. About 5-10% of babies who inhale meconium develop meconium aspiration syndrome.

Signs And Symptoms Of MAS 

The signs and symptoms may appear during the fetal stage if the fetus has expelled meconium inside the uterus. Babies who inhale meconium during labor may display symptoms within a few hours after birth.

Below are some of the common signs and symptoms of meconium aspiration syndrome (1) (5).

  • Green-colored stains or streaks in amniotic fluid
  • Bluish appearance of baby’s skin
  • Low heart rate before birth
  • Limpness in the baby at birth
  • Low Apgar score (used to evaluate a newborn’s skin color, heart rate, reflexes, muscle tone, and breathing rate)
  • Breathing problems that may include rapid breathing (tachypnea), labored breathing (dyspnea), or suspension of breathing (apnea)
  • Grunting sound while breathing
  • Retractions (pulling in) of the chest wall
  • Yellowish nails or skin due to prolonged exposure to meconium

Complications Of Meconium Aspiration Syndrome

Babies with meconium aspiration syndrome usually do not experience long-term health complications. However, babies with severe MAS may have the following complications (1).

Diagnosis Of MAS In Babies 

The diagnosis of meconium aspiration syndrome is dependent on the presence of meconium in the amniotic fluid. The diagnostic procedure may include (2) (3):

  • Observing the fetus for low heart rate
  • Checking for baby’s abnormal breathing sounds (crackly or coarse sounds) using a stethoscope
  • Examining patches or streaky areas on the lungs using chest X-ray
  • Detecting blood acidity, low oxygen levels, and high carbon dioxide levels with blood gas analysis

Treatment For MAS

The treatment of MAS depends on several factors, such as the amount of meconium inhaled, the duration of exposure, and the overall health of the newborn.

A newborn who is active, crying, and breathing normally at birth usually does not require any treatment despite the presence of meconium in the amniotic fluid. The baby will still be kept under observation since MAS symptoms may emerge anytime within 24 hours.

If the newborn displays signs of MAS, such as respiratory distress, low heart rate, and poor muscle tone, the healthcare provider may consider the following interventions (1) (5).

  • Amnioinfusion has been shown to be beneficial for babies who are at high risk due to limited monitoring facilities. Further research into the effects on women is needed and is not practiced regularly. In amnioinfusion, a sterile liquid is infused into the amniotic fluid through a small tube. It will help dissolve meconium and reduce the amount inhaled by the baby.
  • The baby’s mouth and upper airways are suctioned immediately after birth by inserting a tube into the airways through the nose or mouth. However, as per the recent NRP guidelines, direct laryngoscopy and endotracheal suctioning are not routinely required for babies born through MSAF.

Most babies show improvement through the procedures mentioned above. The baby may be placed under observation to rule out relapse of symptoms.

Babies with severe MAS symptoms may undergo the following procedures for further improvement (2) (3).

  • Supplemental oxygen provided through a breathing machine or specialized ventilators
  • Intravenous antibiotics to prevent lung infections
  • Use of radiant warmer to keep the baby’s body temperature in the optimum range
  • Chest physiotherapy where the baby’s chest is tapped periodically to loosen meconium lodged in the alveoli (air sacs)
  • Severe cases may require administration of surfactants to improve lung function and specialized gases, such as nitric oxide, to improve oxygen exchange

The baby will be provided intravenous nutrition in the NICU until their condition improves.

Prognosis Of MAS In Babies 

Most babies may need two to four days of treatment, and the syndrome resolves within a few weeks. Babies with severe MAS may display rapid breathing for a few days after other symptoms resolve. There are usually no long-term effects or lung damage, even in babies with severe symptoms.

In rare cases, a baby may develop persistent pulmonary hypertension (long-term high blood pressure within the lungs), permanent narrowing of the airways, and brain damage due to inadequate oxygen for the brain. Most babies seldom display severe complications since they have growing lungs, which generate new alveoli to facilitate healthy respiration (1).

Prevention Of MAS 

Regular checkups and ultrasonography could help in the early detection of fetal breathing problems indicative of MAS. You may also take the following precautions to avoid the risk of MAS (1) (3).

  • Follow your ultrasonography (ultrasound checks) schedule diligently. It could help in the timely detection of risk factors that lead to premature excretion of meconium, such as problems in the placenta or umbilical cord.
  • Proper management of health conditions during pregnancy, such as diabetes, may help reduce the risk of MAS.
  • Avoid unhealthy habits, such as smoking, during pregnancy.
  • Consult your doctor if you observe green-stained liquid during a water break during pregnancy.

Meconium aspiration syndrome or MAS is an uncommon condition. It is identified at birth through the baby’s breathing pattern, low heart rate, or bluish appearance. The baby may be kept under observation for a few days until they show signs of improvement. Fortunately, MAS has a good prognosis since babies’ lungs are still growing. Also, the condition seldom leads to complications. During pregnancy, frequent health checkups and adhering to a healthy lifestyle could help prevent MAS. Also, if you notice any concerning signs during pregnancy, consult your doctor for prompt medical attention.

Key Pointers

  • Meconium aspiration syndrome (MAS) occurs when the fetus inhales a mixture of meconium and amniotic fluid in-utero.
  • Risk factors may include post-term pregnancy, prolonged labor, diabetes, high blood pressure, or other complications.
  • Long-term health risks are absent in most cases, but babies with severe MAS may have an increased risk of developing chronic lung disorders, neurological problems, and other issues.
  • Amnioinfusion and suctioning of the airways immediately after birth can help reduce the manifestations of MAS.


MomJunction's articles are written after analyzing the research works of expert authors and institutions. Our references consist of resources established by authorities in their respective fields. You can learn more about the authenticity of the information we present in our editorial policy.
1. Meconium aspiration: Johns Hopkins Medicine
2. Meconium aspiration syndrome: Johns Hopkins Medicine
3. Meconium aspiration syndrome: U.S. National Library of Medicine
4. Meconium Aspiration; Children’s Hospital of Philadelphia
5. Meconium aspiration syndrome: Benioff Children’s Hospital
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Dr. Neema Shrestha

Dr. Neema Shrestha is a pediatrician with a special interest in the field of neonatology. Currently working in Kathmandu, Nepal, she completed her MBBS from Kasturba Medical College, Manipal in 2008, Diploma in Child Health from D.Y. Patil University in 2011, MD from Nepal Medical College in 2015 and Fellowship in Neonatology from Sir Ganga Ram Hospital, New Delhi in... more

Dr Bisny T. Joseph

Dr. Bisny T. Joseph is a Georgian Board-certified physician. She has completed her professional graduate degree as a medical doctor from Tbilisi State Medical University, Georgia. She has 3+ years of experience in various sectors of medical affairs as a physician, medical reviewer, medical writer, health coach, and Q&A expert. Her interest in digital medical education and patient education made... more