Meconium Aspiration Syndrome Causes

Quick Answer

Meconium aspiration syndrome (MAS) may occur when a baby’s first feces is passed while still in the womb or soon after delivery. When this happens, the baby is at risk for breathing feces into their lungs. MAS is a leading cause of illness and death in newborns. Learn what causes meconium aspiration syndrome and what legal options you may have if your baby was harmed.

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What Causes Meconium Aspiration Syndrome?

Meconium aspiration syndrome (MAS) is caused by a newborn ingesting or inhaling a mix of amniotic fluid and meconium (a dark green substance that is the baby’s first feces).

A doctor uses a stethoscope to check a newborn's heart.Babies usually pass meconium in the first few hours or days following birth. However, some babies pass meconium while they are still in the womb, which means it gets mixed into the amniotic fluid.

When a baby is under stress, they may forcefully gasp the mixture into their lungs, putting them at risk for meconium aspiration syndrome.

“[Meconium aspiration syndrome] typically occurs when the fetus is stressed during labor, especially when the infant is past its due date.”

—Johns Hopkins Medicine

To follow are some risk factors that contribute to meconium aspiration syndrome causes.

Meconium Aspiration Syndrome Risk Factors

The top risk factor for what causes meconium aspiration syndrome is fetal distress. However, other situations can make MAS more likely to occur.

Some risk factors and causes of meconium aspiration syndrome include:
  • Health issues in the mother: If the baby’s mother has a health issue like diabetes or high blood pressure, the infant is more likely to be stressed before or during birth.
  • Intrauterine growth restriction (IUGR): This occurs when the fetal weight is below the 10th percentile for gestational age.
  • Lack of oxygen: Babies with low oxygen levels are more likely to gasp, which can be what causes meconium aspiration syndrome.
  • Post-term pregnancy: A baby born after their due date may be stressed due to the aging placenta. As a result, they are more likely to pass meconium while still in the womb.
  • Prolonged or difficult delivery: Babies born after a long or hard delivery are more likely to pass meconium due to fetal distress. While in distress, a baby may gasp while still in the womb or soon after delivery.
  • Smoking: Mothers who smoke during pregnancy are more likely to have infants with MAS, potentially due to how tobacco smoke affects the baby’s breathing patterns.

If you have questions about meconium aspiration syndrome causes, our registered labor and delivery nurses are here to help.

Nurse Beth Carter

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Common Symptoms of Meconium Aspiration Syndrome

Symptoms of MAS can vary for each baby, but there are some common ones to watch out for.

Symptoms of meconium aspiration syndrome include:

  • Bluish skin color
  • Body limpness
  • Difficulty breathing (respiratory distress)
  • Grunting when breathing
  • Meconium-stained amniotic fluid
  • Rapid breathing
  • Slow heart rate

How Is Meconium Aspiration Syndrome Diagnosed?

Doctors can diagnose MAS before or shortly after birth with various tests.

Tests to detect meconium aspiration syndrome include:
  • Blood gas analysis: Babies with meconium aspiration syndrome may show signs of low blood acidity, increased carbon dioxide, and decreased oxygen.
  • Chest X-ray: Diagnostic images of babies with meconium aspiration syndrome are likely to show streaky or patchy areas on the lungs.
  • Laryngoscopy: Infants with meconium aspiration syndrome could have stains on the vocal cords. Doctors can use a laryngoscope to look for these stains.

Meconium Aspiration Syndrome Complications

Meconium aspiration syndrome can make it harder for your newborn to breathe.

This is because the inhaled meconium can:

  • Block the airways
  • Injure the baby’s lungs
  • Irritate the airways

If obstetricians fail to diagnose and treat meconium aspiration syndrome in time, MAS may cause permanent lung damage.

In severe cases of meconium aspiration syndrome, the baby may suffer brain damage or even death if there is a prolonged lack of oxygen while they are in the uterus.

Brain damage in babies can lead to the following:
  • Behavioral effects: Brain damage can cause an exaggeration of personality characteristics like anger or agitation.
  • Cognitive effects: Brain injuries can change a child’s thinking, learning, and perceiving ability. Children may have difficulties remembering and understanding events, concepts, and people.
  • Communication problems: Children with brain damage may find communicating through physical movements or spoken language challenging.
  • Physical effects: Brain injuries can cause problems with coordination, mobility, balance, and muscle weakness. They may also develop long-term health issues like chronic lung disease and asthma.

MAS can also cause persistent pulmonary hypertension of the newborn (PPHN). This rare but serious condition affects the blood flow to and from the lungs.

Did You Know

According to Cleveland Clinic, meconium aspiration syndrome is one of the top causes of PPHN.

Sometimes, parents are unaware that their baby suffered from brain damage due to meconium aspiration syndrome. This is because symptoms are not always obvious.

Developmental delays can be an early sign of newborn brain damage. If you suspect your baby may be at risk for brain damage due to MAS, take our free developmental milestone quiz now.


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Treatment for Meconium Aspiration Syndrome

When doctors detect meconium aspiration syndrome, they will suction the baby’s mouth during delivery. The healthcare team will provide further treatment if fetal distress is accompanied by thick meconium staining.

Babies with meconium aspiration syndrome typically need special care in the neonatal intensive care unit (NICU). The healthcare team will give the baby oxygen for breathing difficulties as needed. They may use a CPAP machine, face mask, or breathing tube.

Additional treatments for babies with MAS include:
  • Antibiotics to fight infections
  • Chest tapping to loosen secretions
  • Extracorporeal membrane oxygenation (ECMO) for pumping blood
  • Inhaled nitric oxide for opening blood vessels
  • Surfactant for opening the lungs
  • Warmer to maintain normal body temperature

Most infants with meconium aspiration syndrome recover within several days to a few weeks, depending on the amount of meconium inhaled.

Meconium Aspiration Syndrome and Medical Negligence

Doctors and hospitals should have the medical expertise to treat or diagnose meconium aspiration syndrome promptly. Failure to do so can cause severe problems for the baby, including brain damage or even death.

Did You Know

Severe meconium aspiration syndrome causes illness and death in up to 10% of newborns, according to Johns Hopkins Medicine.

Delivery teams are responsible for spotting signs of meconium aspiration syndrome and suctioning the baby’s airways. Clearing the airways ensures the baby doesn’t experience hypoxemia (lack of oxygen in the blood) or hypoxia (lack of oxygen in the tissues).

Depending on the severity of the baby’s breathing difficulties, the pediatrics team may also have to use mechanical ventilation or a breathing machine to keep the baby’s lungs inflated. Failure to do so could be a sign of medical negligence.

If your child developed severe meconium aspiration syndrome and suffered life-altering injuries as a result of negligence, you may be able to take legal action by filing a medical malpractice claim.

Get a free legal consultation to find out if you can get connected with one of the nation’s best birth injury firms.

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Filing a Meconium Aspiration Syndrome Lawsuit

If your child was harmed due to your obstetrician’s failure to diagnose or treat meconium aspiration syndrome in time, you may be able to take legal action.

Filing a birth injury lawsuit may allow you to recover compensation for:

  • Diminished quality of life for your child
  • Loss of income from missing work
  • Medical expenses and hospital bills
  • Pain and suffering

If your child has a birth injury caused by severe MAS, reach out to the Birth Injury Justice Center. We may be able to help you get justice and financial compensation.

Call (800) 914-1562 or fill out our online form for a free case review.

Meconium Aspiration Syndrome Causes FAQs

Who is at risk for meconium aspiration syndrome?

The main risk factors that lead to meconium aspiration syndrome causes are fetal distress and fetal heart rate irregularities.

What causes a baby to swallow meconium?

A baby may swallow meconium when they are stressed due to a decrease in blood and oxygen. Other causes of fetal distress include health issues of the mother, prolonged childbirth, and post-term delivery.

What causes meconium in amniotic fluid?

When babies are under stress due to a decrease in oxygen and blood supply, they may pass meconium while still in the womb. This causes meconium to mix with the amniotic fluid.

What causes a baby to swallow meconium?

When meconium mixes into the amniotic fluid, a baby is at risk for swallowing it when they take their first breaths during delivery. You may be able to sue for birth injuries caused by your baby swallowing meconium if medical negligence is to blame. See if you can connect with an experienced birth injury lawyer to learn more about your legal options.

Birth Injury Support Team
Reviewed by:Beth Carter, RN

Registered Nurse, Legal Nurse Consultant Certified

  • Fact-Checked
  • Editor

Beth Carter has over 18 years of experience as a Registered Nurse. She spent nearly half of that time working in labor and delivery units. This, combined with her own experience giving birth to a premature baby, ignite Beth’s passion for helping new mothers access the information and resources they deserve.

The Birth Injury Justice Center was founded in 2003 by a team of legal professionals to educate and empower victims and families affected by birth injuries. Our team is devoted to providing you with the best resources and legal information for all types of birth injuries.

View Sources
  1. American Heart Association (2010). “2010 American Heart Association guidelines for cardiopulmonary resuscitation and emergency cardiovascular care: Neonatal resuscitation.” Retrieved April 14, 2023 from
  2. Cleveland Clinic. (2022 August). “Intrauterine Growth Restriction.” Retrieved April 14, 2023 from
  3. Johns Hopkins Medicine. (n.d.) “Meconium Aspiration Syndrome.” Retrieved April 14, 2023 from
  4. National Library of Medicine: MedlinePlus. (n.d.) “Meconium aspiration syndrome.” Retrieved April 14, 2023 from
  5. National Library of Medicine: PubMed Central (2019). Cureus. “Factors Leading To Meconium Aspiration Syndrome in Term- and Post-term Neonates.” Retrieved April 14, 2023 from
  6. National Library of Medicine: PubMed Central (2009). HHS Public Access. “An Epidemiologic Study Comparing Fetal Exposure to Tobacco Smoke in Three Southeast Asian Countries.” Retrieved April 14, 2023 from
  7. Nemours KidsHealth (2020 January). “Meconium Aspiration Syndrome (MAS).” Retrieved April 14, 2023 from
  8. Persistent pulmonary hypertension in the neonate (PPHN). Cleveland Clinic. (n.d.). Retrieved May 1, 2023, from
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