Meconium aspiration

Alternative names:

meconium aspiration syndrome (MAS)

Definition:

Meconium is the first feces (stool) of the newborn. It is thick, sticky, and greenish-black in color. Aspiration occurs when the newborn inhales the meconium mixed with amniotic fluid during labor and delivery.

Causes, incidence, and risk factors:

Meconium aspiration typically occurs when the fetus is stressed during labor. The infant is often post term (more than 40 weeks gestation).

During the stressful labor, the infant may suffer a lack of oxygen. This can cause increased movement of the intestines (peristalsis) and relaxation of the anal sphincter, resulting in passage of meconium into the amniotic fluid surrounding the unborn baby. The amniotic fluid and meconium mix to form a green stained fluid of various thickness (viscosity). If the infant breathes while still in the uterus or when the baby takes its first breath, the meconium/amniotic fluid mixture can be inhaled into the lungs. The inhaled meconium can cause a partial or complete blockage of the airways, causing difficulty breathing and poor gas exchange in the lungs. In addition, it is irritating and causes inflammation in the airways and a type of pneumonia.

Meconium staining of the amniotic fluid with possibility of aspiration occurs in approximately 5 percent to 10 percent of births. About one third of the infants with meconium aspiration will require some type of assisted breathing. Meconium aspiration is a leading cause of severe illness and death in the newborn. Risk factors include: being post-term, difficult deliver, fetal distress and intra-uterine hypoxia (decreased oxygen to the infant while still in the uterus).