Meconium Aspiration Syndrome


Meconium aspiration syndrome (MAS) is a set of symptoms that happen when an infant inhales meconium. Meconium is the first stool of an infant. It is sometimes passed into the fluid that surrounds the baby in the womb.


Not all infants who inhale meconium will have MAS. It is not known why some infants get MAS and others do not.

Risk Factors

Things that may raise a baby’s risk of meconium aspiration are:

  • Delivery after 42 weeks
  • Cesarean section delivery
  • Abnormal heart rate during labor
  • Low levels of amniotic fluid
  • Low or high birth weight
  • Meconium below the baby’s vocal cords

Things in a mother that may raise the chance of meconium aspiration in the baby are:

Gestational Diabetes

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MAS may cause:

  • Breathing that is too fast or too slow
  • Blue skin color
  • Grunting
  • Nostrils that spread out when breathing
  • Low muscle tone or muscle spasms


This problem is diagnosed in a newborn based on symptoms and signs of meconium in the fluid. The diagnosis can be confirmed with a chest x-ray. Blood tests will also be done.


The overall goal of treatment is to promote breathing. This can be done with:

  • Intubation to open the airway and suction it as needed
  • Oxygen therapy to ease breathing
  • Breathing support in babies who cannot breathe on their own


Medicines that may be used are:

  • Antibiotics to treat infection
  • Surfactants to coat the lungs, clear the airways, and help the lungs mature
  • Nitric oxide gas to open blood vessels in the lungs to let more oxygen in the body


There are no methods to prevent MAS.


Healthy Children—American Academy of Pediatrics
Kids Health—Nemours Foundation


About Kids Health—The Hospital for Sick Children
Caring for Kids—Canadian Paediatric Society


Chettri S, Bhat BV, et al. Current Concepts in the Management of Meconium Aspiration Syndrome. Indian J Pediatr. 2016 Oct;83(10):1125-1130.
Meconium aspiration. Kids Health—Nemours Foundation website. Available at:
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Updated November 2019. Accessed December 31, 2019.
Meconium aspiration syndrome. EBSCO DynaMed website. Available at: Updated August 24, 2018. Accessed December 31, 2019.
Last reviewed September 2019 by EBSCO Medical Review Board Kari Kassir, MD
Last Updated: 5/29/2020

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