Meconium Aspiration Syndrome

Meconium is the first feces of a newborn that is stored in the baby's intestines until birth. Although it is different from regular stool because it doesn't have any bacteria or odor, it can cause problems if a baby inhales the meconium while in the uterus, when it is mixed with amniotic fluid, or just after they are born. When this occurs, it is called meconium aspiration. This usually happens in babies born on time and those born post-term, after 42 weeks, as opposed to premature infants.

When meconium is found in the amniotic fluid, the doctors take special precautions to prevent aspiration. Most babies with meconium passage are treated with these precautions and breath just fine and never develop further problems. However, there is a small group of these infants that can become quite sick, even when all precautions are taken.

Meconium particles in the amniotic fluid can block small airways and prevent a baby from breathing properly, causing respiratory distress. This meconium aspiration can occur either during labor or at the time of a baby's first breaths. If this occurs, some babies may require the help of a mechanical breathing machine. Infection also can occur and cause pneumonia.

Furthermore, some babies with meconium aspiration go on to develop a condition called pulmonary hypertension. Pulmonary hypertension decreases the flow of blood into the lungs, where it normally picks up oxygen. Instead, blood by-passes the lungs, and very little oxygen gets to the baby. The condition often improves within a few days, although severe meconium aspiration and pulmonary hypertension may be fatal in a very small percentage of babies.

Experts at UCSF Children's Hospital care for infants in the William H. Tooley Intensive Care Nursery.

Reviewed by health care specialists at UCSF Children's Hospital.
Last updated May 8, 2007