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Meconium aspiration   

Overview | Symptoms | Treatment | Prevention

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 and may be seen in the amniotic fluid after 34 weeks gestation. Aspiration occurs when the newborn inhales the meconium mixed with amniotic fluid either in the uterus or just after delivery.

Causes and Risks

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

During 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 chemical pneumonia.

Meconium staining of the amniotic fluid with possibility of aspiration occurs in approximately 5% to 10% 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: post-term pregnancy, preeclampsia, maternal diabetes, maternal hypertension, difficult delivery, fetal distress and intra-uterine hypoxia (decreased oxygen to the infant while still in the uterus).

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