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Meconium aspiration syndrome

MAS; Meconium pneumonitis (inflammation of the lungs); Labor - meconium; Delivery - meconium; Neonatal - meconium; Newborn care - meconium

Meconium aspiration syndrome (MAS) refers to breathing problems that a newborn baby may have when:

  • There are no other causes, and
  • The baby has passed meconium (stool) into the amniotic fluid during labor or delivery

MAS may occur if the baby breathes in (aspirates) this fluid into the lungs.


Meconium is the early feces (stool) passed by a newborn soon after birth. It is passed from the body before the baby has started to digest breast milk (or formula).

In some cases, the baby passes meconium while still inside the uterus. This will happen when babies are "under stress" because their supply of blood and oxygen decreases. This is often due to problems with the placenta or the umbilical cord.

Once the meconium has passed into the surrounding amniotic fluid, the baby may breathe meconium into the lungs. This may happen while the baby is still in the uterus, or still covered by amniotic fluid after birth. The meconium can also block the infant's airways right after birth.

It can cause breathing problems due to swelling (inflammation) in the baby's lungs after birth.

Risk factors that may cause stress on the baby before birth include:

  • "Aging" of the placenta if the pregnancy goes far past the due date
  • Decreased oxygen to the infant while in the uterus
  • Diabetes in the pregnant mother
  • Difficult delivery or long labor
  • High blood pressure in the pregnant mother

Some babies do not breathe the meconium fluid into their lungs during labor and delivery. They are unlikely to have any symptoms or problems.

Babies who do breathe in this fluid may have the following:

  • Bluish skin color (cyanosis) in the infant
  • Working hard to breathe (noisy breathing, grunting, using extra muscles to breathe, breathing rapidly)
  • No breathing
  • Limpness at birth
Exams and Tests

Before birth, the fetal monitor may show a slow heart rate. During delivery or at birth, meconium can be seen in the amniotic fluid and on the infant.

The infant may need help with breathing or heartbeat right after birth, and may have a low Apgar score.

The health care team will listen to the infant's chest with a stethoscope and may hear abnormal breath sounds, especially coarse, crackly sounds.

A blood gas analysis will show low (acidic) blood pH, decreased oxygen, and increased carbon dioxide.

A chest x-ray may show patchy or streaky areas in the infant's lungs.


A special care team should be present when the baby is born if traces of meconium are found in the amniotic fluid. This happens in more than 10% of normal pregnancies. If the baby is active and crying, no treatment is needed.

If the baby is not active and crying right after delivery, a tube is placed in the infant's airway by a nurse, therapist, or doctor. Suction is used to remove any meconium. This procedure may be repeated more than once.

If the baby is not breathing or has a low heart rate:

  • The team will help the baby breathe using a face mask attached to a bag that delivers an oxygen mixture to inflate the baby's lungs.
  • The infant may be placed in the special care nursery or newborn intensive care unit in order to be watched closely.

Other treatments may include:

  • Antibiotics to treat infection.
  • Breathing machine (ventilator): Not commonly needed. Many problems can develop while the child is using a breathing machine.
  • Oxygen to keep blood levels normal.
  • Radiant warmer to maintain body temperature.
  • Surfactant to help lungs exchange oxygen.
  • Nitric oxide (also referred to as NO, an inhaled gas) to help blood flow and oxygen exchange in the lungs.
  • ECMO (extracorporeal membrane oxygenation) is a kind of heart/lung bypass. It may be used in very severe cases.
Outlook (Prognosis)

In most cases, the outlook is excellent and there are no long-term health effects.

  • Only about half of babies with meconium stained fluid will have breathing problems and only about 5% will have MAS.
  • Breathing problems may be more severe in some cases. These will often go away in 2 to 4 days. However, rapid breathing may continue for several days.
  • MAS rarely leads to permanent lung damage.

Meconium may be present at birth in the amniotic fluid because there is a serious problem with the blood flow to and from the lungs. This is called persistent pulmonary hypertension of the newborn (PPHN).


Staying healthy during pregnancy and following your health care provider's advice can often prevent problems that lead to meconium being present.

Your providers will want to be prepared for meconium being present at birth if:

  • Your water broke at home and the fluid was clear or stained with a greenish or brown substance.
  • Any testing done during your pregnancy indicates there may be problems present.
  • Fetal monitoring shows any signs of fetal distress can be found early.


Crowley MA. Neonatal respiratory disorders. In: Martin RJ, Fanaroff AA, Walsh MC, eds. Fanaroff and Martin's Neonatal-Perinatal Medicine. 10th ed. St. Louis, MO: Elsevier Saunders; 2015:chap 74.

Waldemar AC, Ambalavanan N. Respiratory tract disorders. In: Kliegman RM, Stanton BF, St Geme JW III, Schor NF, eds. Nelson Textbook of Pediatrics. 20th ed. Philadelphia, PA: Elsevier; 2016:chap 101

Wyckoff MH, Aziz K, Escobedo MB, Kapadia VS. Part 13: Neonatal Resuscitation: 2015 American Heart Association Guidelines Update for Cardiopulmonary Resuscitation and Emergency Cardiovascular Care. Circulation. 2015; 3;132(18 Suppl 2):S543-560.


Review Date: 11/3/2015

Reviewed By: Kimberly G Lee, MD, MSc, IBCLC, Associate Professor of Pediatrics, Division of Neonatology, Medical University of South Carolina, Charleston, SC. Review provided by VeriMed Healthcare Network. Also reviewed by David Zieve, MD, MHA, Isla Ogilvie, PhD, and the A.D.A.M. Editorial team.

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