What Is Meconium Aspiration Syndrome (MAS)? - Long-Term Effects & Treatment

Instructor: Sarah Lawson

Sarah has taught nursing courses and has a master's degree in nursing education.

Meconium Aspiration Syndrome (MAS) is a potentially serious medical condition that affects newborn infants. Learn more about MAS, its long-term effects and treatment.

What is Meconium Aspiration Syndrome (MAS)?

Every new parent-to-be dreams of a perfect delivery of a healthy newborn baby. They imagine meeting their baby and the amazing joy they will feel holding him or her for the first time. They anticipate the excitement of introducing their precious bundle of joy to friends and family. They wonder whose nose the baby will have.

One thing most parents don't anticipate happening is complications during or after the delivery. Sometimes during labor there is additional stress on the infant. This stress can cause the infant to pass the first stool called meconium in the womb. This occurs in 5-20% of all births.

Normally, amniotic fluid is clear. When a baby passes stool in the womb, amniotic fluid becomes green or yellow-tinted. This by itself is not a problem. The problem occurs when the baby gasps or breaths in this meconium contaminated amniotic fluid. This can occur before birth or while the baby is being born.

Meconium aspiration syndrome (MAS) occurs when meconium is present in the baby's lungs. This can cause respiratory problems for the baby. Of the cases where meconium is present in the amniotic fluid, less than 5% will develop MAS.

First stool, called meconium
Babys first stool called meconium

Signs and Symptoms

During labor, one of the first assessments made is examining the color of the amniotic fluid if the woman's membranes have ruptured. If the amniotic fluid is green or yellow-tinted, the examiner knows that meconium is present. Knowing if meconium is present in the fluid helps doctors and nurses to take extra precautions before the actual delivery. These precautions often include additional staff and equipment in case resuscitation efforts are necessary.

Remember earlier how I said having meconium contaminated amniotic fluid by itself is not a problem? Just because the fluid is stained, does not mean the baby has breathed it in. Examiners will check the baby for the following signs and symptoms that suggest MAS:

  • Rapid breathing
  • Barrel-chest
  • Low Apgar score (Appearance, Pulse, Grimace, Activity, and Respiration)
  • Cyanosis (blue color of skin)

MAS can be confirmed with several tests or exams. A stethoscope may be used to listen for abnormal lung sounds, such as crackles (wet sounds) and rhonchi. Rhonchi are course rattling sounds caused by secretions in the bronchial airway.

A blood gas test would show respiratory acidosis. Respiratory acidosis is a condition in which hypoventilation is causing increased carbon dioxide in the blood. This is a sign of respiratory distress syndrome, a decreased ability of the infant's lung to provide necessary oxygen to the body due to immaturity of lung development. This condition often requires ventilator support.

A chest x-ray would show patchy or streaked areas in the lungs.

Chest x-ray of infant with respiratory distress syndrome
Chest x-ray of infant with respiratory distress syndrome (RDS)


Fetal distress during labor, usually from hypoxia or low oxygen saturation in the blood, is normally the cause of meconium passing before birth. This causes the baby's intestines to contract as well as the anal sphincter to relax and allow meconium to pass. However, MAS will only occur if the baby gasps or breathes in this meconium contaminated amniotic fluid before or during birth. Other causes associated with MAS include:

  • A long or difficult labor and delivery
  • Advanced gestational age (over 40 weeks)
  • A mother who smokes cigarettes heavily
  • Gestational diabetes, high blood pressure, or chronic respiratory disease in the mother
  • Umbilical cord compression or complications
  • Poor intrauterine growth of the baby


Standard treatment used to involve suctioning of the infant's mouth and nose at the delivery of the head. New research has shown this practice to not be effective and is no longer recommended. However, when a baby is born with meconium-stained fluids and is showing signs of distress, a laryngoscope and endotracheal tube may be used to deep suction below the baby's vocal cords to remove meconium. Additional treatments may include:

  • Antibiotics if infection is suspected
  • Breathing machine if baby has respiratory distress syndrome and requires ventilation
  • Warmer to maintain baby's body temperature
  • Tapping on baby's chest to help loosen secretions

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