Meconium Aspiration Syndrome
Every parent-to-be hopes for an uncomplicated birth and a healthy baby. But some babies do face delivery room complications. One that may affect a newborn's health is meconium aspiration, also referred to as meconium aspiration syndrome (MAS). Although it can be serious, most cases of MAS are not.

MAS can happen before, during, or after labor and delivery when a newborn inhales (or aspirates) a mixture of meconium and amniotic fluid (the fluid in which the baby floats inside the amniotic sac). Meconium is the baby's first feces, or poop, which is sticky, thick, and dark green and is typically passed in the womb during early pregnancy and again in the first few days after birth.

The inhaled meconium can partially or completely block the baby's airways. Although air can flow past the meconium as the baby breathes in, the meconium becomes trapped in the airways when the baby breathes out. The meconium irritates the baby's airways and makes it difficult to breathe.

MAS can affect the baby's breathing in a number of ways, including chemical irritation to the lung tissue, airway obstruction by a meconium plug, infection, and the inactivation of surfactant by the meconium (surfactant is a natural substance that helps the lungs expand properly).

The severity of MAS depends on the amount of meconium the baby inhales as well as underlying conditions, such as infections within the uterus or postmaturity (when a baby is overdue, or more than 40 weeks gestational age). Generally, the more meconium a baby inhales, the more serious the condition.