Meconium is a dark green fecal material produced in the intestines of a fetus before birth. After delivery, your newborn will pass meconium stools for the first few days of life.

Stress that your baby experiences before or during birth may cause your baby to pass meconium stool while still in the uterus. The meconium stool then mixes with the amniotic fluid that surrounds the fetus.

Your baby may then breathe the meconium and amniotic fluid mixture into their lungs shortly before, during, or right after birth. This is known as meconium aspiration or meconium aspiration syndrome (MAS).


MAS may occur when your baby experiences stress. Stress often results when the amount of oxygen available to the fetus is reduced. Common causes of fetal stress include:

  • a pregnancy that goes past the due date (more than 40 weeks)
  • difficult or long labor
  • certain health issues experienced by the mother, including hypertension (high blood pressure) or diabetes
  • an infection

The fetus doesn’t begin to produce meconium until later in pregnancy, so as a pregnancy goes past its due date, the fetus has the potential to be exposed to meconium for a longer period of time.

As pregnancy progresses to term and beyond, the amount of amniotic fluid is also decreased, which concentrates the meconium. As a result, MAS is more common in overdue newborns as compared to term newborns. MAS is rare in preterm newborns.

Respiratory distress is the most prominent symptom of MAS. Your infant may breathe rapidly or grunt during breathing. Some newborns may stop breathing if their airways are blocked by meconium. Your baby may also exhibit the following symptoms:

  • a bluish skin color, which is called cyanosis
  • limpness
  • low blood pressure

A diagnosis is made based on your newborn’s symptoms and the presence of meconium in the amniotic fluid.

Your doctor will listen to your infant’s chest with a stethoscope to detect sounds of abnormal breathing. There are a few methods commonly used to confirm the diagnosis:

  • blood gas test to evaluate oxygen and carbon dioxide levels
  • chest X-ray to see if material has entered your newborn’s lungs

If MAS occurs, your newborn will need immediate treatment to remove the meconium from the upper airway. After delivery, your doctor will immediately suction the nose, mouth, and throat.

If your baby isn’t breathing or responding well, a tube may be placed in your newborn’s windpipe (trachea) to suction the fluid containing meconium from the windpipe. The suctioning may then continue until no meconium is seen in the material removed.

If your newborn still isn’t breathing or has a low heart rate, your doctor will use a bag and mask to help them breathe. This will deliver oxygen to your baby and help inflate their lungs.

Your doctor may need to place a tube in your newborn’s windpipe to help them breathe if the infant is very ill or isn’t breathing on their own.

After emergency treatment has been provided, your newborn may be placed in a special care unit to observe their breathing. Additional treatment may be needed to avoid complications of MAS. Five common treatments include:

  • oxygen therapy to make sure there is enough oxygen in the blood
  • the use of a radiant warmer to help your baby maintain body temperature
  • antibiotics such as ampicillin and gentamicin to prevent or treat an infection
  • the use of a ventilator (a breathing machine) to help your infant breathe
  • extracorporeal membrane oxygenation (ECMO) if your baby isn’t responding to other treatments or has high blood pressure in the lungs (for this treatment, a pump and machine that performs the function of the lungs do the work of your newborn’s heart and lungs so that these organs can heal)

Most newborns with MAS won’t have any long-term health complications. However, MAS is a serious issue that can have an immediate impact on your newborn’s health. Meconium in the lungs can cause inflammation and infection.

Meconium can also block the airways, which can cause lung over expansion. If a lung over expands or inflates too much, it can rupture or collapse. Then air from inside the lung can accumulate in the chest cavity and around the lung. This condition, known as a pneumothorax, makes it difficult to reinflate the lung.

MAS increases the risk of your infant developing persistent pulmonary hypertension of the newborn (PPHN). High blood pressure in the vessels of the lungs restricts blood flow and makes it difficult for your baby to breathe properly. PPHN is a rare but life-threatening condition.

On rare occasions, severe MAS may limit oxygen to the brain. This may cause permanent brain damage.

Infants who experience mild complications of MAS usually recover well. Infants who develop brain damage or PPHN as a result of MAS may face lifelong health issues that require medical support.

Early detection is the best defense in preventing MAS. Fetal monitoring before delivery can determine whether your baby is experiencing stress.

Your doctor can take steps to alleviate fetal distress during labor and reduce the potential for MAS to develop. And if your baby is experiencing stress, your doctor will be prepared to evaluate and treat your baby right away if there are signs of MAS.