The possibility of inhaling meconium occurs in about 5-10% of births. It typically occurs when the fetus is stressed during labor, especially when the infant is past its due date. The condition is serious -- meconium aspiration is a leading cause of severe illness and death in the newborn. During a stressful labor, an infant may suffer a lack of oxygen. This can cause increased movement of the infant's intestines and relaxation of the anal sphincter, causing meconium to pass into the amniotic fluid surrounding the unborn baby. The amniotic fluid and meconium mix to form a green-stained fluid of various thickness. Meconium itself is thick, sticky, and greenish-black in color. If the infant breathes while still in the uterus or while still covered by this fluid after birth, the mixture of meconium and amniotic fluid can be inhaled into the lungs. The inhaled meconium can partially or completely block the infant's airways. The infant has difficulty breathing and poor gas exchange in the lungs. In addition, the substance is irritating and causes inflammation in the airways and, potentially, chemical pneumonia. About one-third of the infants with meconium aspiration will require some type of assisted breathing. Risk factors include maternal diabetes, maternal hypertension, difficult delivery, fetal distress, and intra-uterine hypoxia (decreased oxygen to the infant while it is still in the uterus).
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