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Meconium Aspiration Syndrome

Signs, Symptoms and Treatment of MAS

By Lisa A. Goldstein

Passing meconium in utero is quite common, according to Dr. Aaron Hamvas, director of the Neonatal Intensive Care Unit at St. Louis Children's Hospital in St. Louis, Mo. "Probably 10 to 20 percent of deliveries have it," he says. "Meconium aspiration itself, that is, getting it in the lungs, though, is quite rare, and the severe forms of it are still rarer. Meconium aspiration tends to be more common in very post-term pregnancies – those greater than 41 weeks."

Dr. Hirschman says that even if infants do aspirate the meconium below their vocal cords, not all will develop respiratory distress. MAS will complicate about 5 percent of meconium-stained deliveries, he says.

Unfortunately, this is one of those things where there's no clear culprit. Most of the time, it's unknown what causes a fetus to be stressed enough to pass meconium, Dr. Hamvas says. Sometimes it results from lack of blood flow to the fetus, either from placental problems or from the umbilical cord getting occluded.

Dr. Hirschman also cites excessive head compression during labor as another possible cause. He points out that although it is often assumed that the newborn inhales the meconium in its first breath after delivery, many infants who develop the syndrome have already aspirated the stained amniotic fluid in utero through fetal gasping, also brought on by stress.

Thankfully, we've come a long way in the past 40 years. While we have more resources at our disposal, unfortunately once the meconium has reached the lungs, much of the damage is done – as shown by the early onset of respiratory distress, Dr. Hirschman says.

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