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Meconium aspiration syndrome (MAS), sometimes referred to as neonatal aspiration of meconium, is a medical condition that affects newborns born with stool, called meconium, that has gotten into their lungs.
If not detected and treated quickly, MAS can potentially lead to serious medical conditions, as well as permanent disorders such as cerebral palsy.
About Meconium Aspiration Syndrome
According to a clinical study published by the U.S. National Institutes of Health, meconium “contains residues of bile, intestinal juice, swallowed amniotic fluid containing lanugo hair, and chemical substances like lipids, carbohydrates, nitrogen, and electrolytes.” 
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Every newborn will have meconium. It’s a normal finding in the first hours to days after birth when babies have their first few stools. Some babies, however, release stool while still in the womb or during the childbirth process.
When a baby stools while still in the womb, it can inhale the meconium when taking the first breaths. This is called aspiration and can lead to breathing difficulties from blockages in the airways. When this occurs, the condition is called meconium aspiration syndrome.
Meconium Aspiration Causes
MAS is primarily caused by fetal distress. Fetal distress can develop due to birth infections, difficult labor, an abnormal fetal heart rate, or umbilical blood flow issues. 
When a baby is in distress, oxygen levels in the blood can decrease, which in turn causes an increase in intestinal activity. The baby’s anal sphincter will begin to relax and release meconium. The meconium then mixes in with the amniotic fluid surrounding the infant.
Johns Hopkins reports that, while around 6–25% of all newborns have “meconium-stained amniotic fluid,” about 11% will develop MAS. 
MAS During Labor
If a baby releases meconium during the labor process, it usually means that the infant is undergoing a long, difficult delivery. Other reasons meconium releases during labor include:
- The baby’s age (when a baby passes its due dates, the advanced gestational age increases the chances of stool being released during delivery)
- Umbilical cord problems, such as the cord being wrapped around the baby’s neck or having a knot in the cord
- Maternal smoking and/or drug use
- A mother with diabetes, high blood pressure, or respiratory problems
- Poor fetal growth (infants small for their gestational age)
Meconium Aspiration Symptoms
Physicians notice the following issues when a baby has meconium aspiration. Not all infants will have every symptom, and some will have more signs and symptoms than others.
- Dark stains mixed in the amniotic fluid, typically brown or dark green
- Green or blue staining on the infant’s skin
- Yellow nails and skin
- Breathing difficulties, grunting sounds, rapid breathing
- Low heart rate prior to birth
- Limp limbs
- Distended chest
- Low Apgar score
- Green urine
- Low fetal blood pressure
Meconium Aspiration Treatment
If MAS is detected, doctors should begin treatment immediately. If breathing issues are identified, physicians may need to perform intubation of the infant. This procedure is when a laryngoscope is inserted into the baby’s trachea. Then endotracheal suctioning can be done to remove as much meconium as possible from the airway. 
Afterward, the medical team will carefully monitor the infant’s breathing, heartbeat, and general health. As part of the management of meconium aspiration, a physician will usually order tests such as X-rays and a blood gas analysis, which help to see if the baby is getting enough oxygen.
Many babies with MAS will heal within a few days after treatment. Infants with severe MAS will need additional treatment, which could include antibiotics, oxygen therapy, being on a ventilator, nitric oxide inhalation treatment, and additional blood tests.
Some babies with severe aspiration will have an artificial type of surfactant placed into their lungs to help keep the air sacs open. This is known as surfactant therapy.  Other babies may need special ventilators with nitric oxide for treatment.
Meconium Aspiration Complications
Babies who are severely affected by MAS will have a chemical irritation of the airways caused by the meconium. If this persists over time, the inflammation leads to lung injury. Long-term respiratory complications from meconium aspiration can manifest as an oxygen requirement, severe asthma-like symptoms, poor growth, and frequent cases of viral or bacterial pneumonia.
Most infants recover from MAS if treated by an experienced medical team who acts quickly. Sometimes, a lack of action by doctors or a misdiagnosis can cause severe medical complications.
For instance, if a doctor detects meconium aspiration but fails to continually monitor the infant after birth, subsequent breathing problems could result in associated medical problems.
Babies who are deprived of oxygen for too long can develop brain damage, which can lead to cerebral palsy, seizures, hypoxic-ischemic encephalopathy (HIE), and even stroke.
Something to Consider
Although most cases of MAS will resolve successfully, it is considered a serious disorder, according to the U.S. Institutes of Health, with both “antepartum as well as intrapartum” causes. 
It’s ultimately your doctor’s responsibility to continuously monitor your baby before, during, and after delivery for fetal stress and other signs. However, pregnant women should remember to always keep prenatal appointments and speak directly to their physicians if any concerns about their baby’s health and well-being arise.
- Meconium aspiration syndrome : A clinical study. (2017, June 26). PubMed Central (PMC).
Retrieved from: https://www.ncbi.nlm.nih.gov/pmc/articles/PMC5531208/
- Meconium Aspiration. (n.d.). Johns Hopkins All Children's Hospital.
Retrieved from: https://www.hopkinsallchildrens.org/Patients-Families/Health-Library/HealthDocNew/Meconium-Aspiration
- Parer, J. T., & Livingston, E. G. (1990, June 16). What Is Fetal Distress? PubMed. National Center for Biotechnology Information.
Retrieved from: https://pubmed.ncbi.nlm.nih.gov/2193513/
- Advances in the management of meconium aspiration syndrome. (2011, November 22). PubMed Central (PMC). U.S. National Institutes of Health.
Retrieved from: https://www.ncbi.nlm.nih.gov/pmc/articles/PMC3228378/
- Goel, A., & Nangia, S. (2016, September 9). Meconium aspiration syndrome: Challenges and solutions. Dove Medical Press - Open Access Publisher of Medical Journals.
Retrieved from: https://www.dovepress.com/meconium-aspiration-syndrome-challenges-and-solutions-peer-reviewed-fulltext-article-RRN
- Prevention of meconium aspiration syndrome: An update and the Baylor experience. (2009, April 22). PubMed Central (PMC). U.S. National Institutes of Health.
Retrieved from: https://www.ncbi.nlm.nih.gov/pmc/articles/PMC2666857/