Meconium aspiration syndrome


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

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


Meconium is the early stool passed by a newborn soon after birth, before the baby starts to feed and digest milk or formula.

In some cases, the baby passes meconium while still inside the uterus. This can happen when babies are "under stress" due to a decrease in blood and oxygen supply. This is often due to problems with the placenta or the umbilical cord.

Once the baby passes the meconium into the surrounding amniotic fluid, they may breathe it into the lungs. This may happen:

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:


Most babies who have passed meconium into the amniotic fluid do not breathe it 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:

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. They may have a low Apgar score.

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

A blood gas analysis will show:

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, the team will:

This intervention is often all babies need to begin breathing on their own.

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

Other treatments may include:

Outlook (Prognosis)

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

MAS can be seen along with a serious problem with the blood flow to and from the lungs. This is called persistent pulmonary hypertension of the newborn (PPHN).


To prevent problems that lead to meconium being present, stay healthy during pregnancy and follow your health care provider's advice.

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

Review Date: 9/29/2019
Reviewed By: Kimberly G. Lee, MD, MSc, IBCLC, Clinical 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, Medical Director, Brenda Conaway, Editorial Director, and the A.D.A.M. Editorial team.

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