Meconium aspiration syndrome

Alternative Names

MAS; Meconium pneumonitis (inflammation of the lungs)

Definition of Meconium aspiration syndrome

Meconium aspiration syndrome is a serious condition in which a newborn breathes a mixture of and amniotic fluid into the lungs around the time of delivery.

Causes, incidence, and risk factors

Meconium is the term used for the early feces (stool) passed by a newborn soon after birth, before the baby has started to digest breast milk (or formula).

Signs 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 delivering obstetrician or midwife should suction the newborn’s mouth as soon as the head emerges during delivery.

Expectations (prognosis)

Meconium aspiration syndrome is a leading cause of severe illness and death in newborns.


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, Medical Director, A.D.A.M., Inc. – 12/10/2009

ADAM Medical Encyclopedia

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