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Clinical features and diagnosis of meconium aspiration syndrome

Joseph A Garcia-Prats, MD
Section Editor
Richard Martin, MD
Deputy Editor
Melanie S Kim, MD


Meconium aspiration syndrome (MAS) is defined as respiratory distress in newborn infants born through meconium-stained amniotic fluid (MSAF) whose symptoms cannot be otherwise explained [1]. MAS can present with varying degrees of severity from mild respiratory distress to life-threatening respiratory failure.

The clinical features and diagnosis of MAS will be discussed here. The management and complications of MAS are discussed elsewhere. (See "Prevention and management of meconium aspiration syndrome".)


In the United States, a retrospective multicenter study of 162,075 term infants born between 1997 and 2007 reported 1.8 percent of infants had an admission diagnosis of MAS [2].

MAS occurs in approximately 2 to 10 percent of infants born through meconium-stained amniotic fluid (MSAF). This was illustrated in a study from a single tertiary center of 20,047 live births between 1994 and 1998 that reported MSAF occurring in 9.2 percent and MAS in 0.1 percent of all live births [3].

This 10-fold difference in the incidence of MAS may be due to differences between the two studies in the rigor that MAS was diagnosed and measures used to prevent MAS. (See "Prevention and management of meconium aspiration syndrome", section on 'Prevention'.)

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Literature review current through: Nov 2017. | This topic last updated: Aug 17, 2017.
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