Meconium aspiration syndrome, or MAS, occurs when a fetus inhales fecal material—called meconium—into the lungs from the surrounding amniotic fluid.
Meconium is the term for the dark green, thick stool that a newborn usually passes in utero or soon after birth. It is composed of amniotic fluid, fecal material, and shed hair and waxy material that covers a fetus during development. If inhaled, meconium can block the airways or cause the lungs to swell, making breathing difficult for the newborn baby. It typically occurs when the fetus is stressed during labor especially for deliveries that are post due date.
Although MAS can be dangerous, in most cases MAS does not result in any long-term lung damage or complications. The severity depends on how much meconium was inhaled and how quickly the baby is treated. Fortunately, most newborns improve within a few days.
In very rare cases, a prolonged lack of oxygen can result in brain damage.
MAS is diagnosed after birth by one or more methods. A doctor may notice dark green stains in the amniotic fluid or on the baby’s skin. Rapid, labored breathing can indicate MAS.
Other signs of MAS include a low Apgar score. An Apgar is a quick test given to newborn babies to measure their heartbeat, color, reflexes, breathing and muscle tone. A blood test may be given to check the baby’s oxygen, pH and carbon dioxide levels. A result that shows decreased oxygen and low blood pH, as well as higher levels of carbon dioxide, can indicate the baby has MAS.
A baby is at risk for releasing meconium in the womb when it is under stress, which can have a number of causes:
- If the mother has diabetes or high blood pressure
- Pregnancies that last far beyond the due date
- Heavy smoking by the mother
- Decreased oxygen to the baby in the uterus (usually due to umbilical cord issues)
- Poor growth of the baby
- A prolonged labor or delivery
A baby with MAS may be brought to a neonatal intensive care unit (NICU) for close observation. The baby may receive a number of treatments, such as oxygen therapy, antibiotics, and the blood may be tested regularly to monitor oxygen levels.
A type of surfactant may be given as well. This is a mixture of proteins and fats produced by the lungs to keep the air sacs from sticking together during exhalation. A modified natural surfactant can be given to ease breathing.
Although MAS is a serious condition, most newborns recover without any long-term issues.
Reviewed by Dr. Jen Lincoln, April 2020
- While dangerous, the ingestion of meconium does not usually result in any long-term complications.
- A baby can be at risk for MAS if the pregnancy lasts far beyond the due date and if the mother is a heavy smoker.
- Babies with MAS typically receive treatment in the NICU through antibiotics and oxygen therapy.