Dr. Greene's Answer
Meconium, the dark-green tarry substance that fills a baby’s intestines up until birth, is a mixture of hair, cells, enzymes, blood, mucus, and other secretions. Meconium is sterile — very unlike the bacteria-filled stools that will follow.
Unfortunately, meconium can cause significant problems if it is inhaled into the lungs. In only about 2% to 5% of babies born in meconium-stained amniotic fluid will some of the thick, tarry meconium be inhaled, plug the small airways, and thus cause respiratory distress (Manual of Pediatric Practice, WB Saunders, 1998 and Nelson Textbook of Pediatrics, WB Saunders, 2007). Speedy delivery of distressed babies and suctioning the mouth and nose when the head has been delivered (before the expanding lungs take their first breath) can help prevent this meconium aspiration. Sometimes, more vigorous suctioning or even infusing extra amniotic fluid into the uterus before birth is needed.
Up to 30% of kids who develop meconium aspiration pneumonias need to go on mechanical ventilators. A few of these have some residual lung problems (wheezing, coughing) even 5 or 10 years later and a small number die from meconium aspiration (Textbook of Pediatrics, WB Saunders, 2007).