Meconium aspiration syndrome is a medical condition affecting newborn infantsin which meconium (first stool of an infant, composed of materials ingested during the time the infant spends in the uterus)is present in their lungs during or before delivery. Fetal distress during labor causes intestinal contractions, as well relaxation of the anal sphincter, which allows meconium to pass into the amniotic fluid.Meconium passage into the amniotic fluid occurs in about 5-20 percent of all births and more common after passing the term.Of the cases where meconium is found in the amniotic fluid, meconium aspiration syndrome develops less than 5 percent of the time.Amniotic fluid is usually clear, but if its mixed with meconium it will become greenish.
The most obvious sign that meconium has been passed during or before labor is the greenish or yellowish appearance of the amniotic fluid. The infant's skin, umbilical cord, or nailbeds may be stained green if the meconium was passed a considerable amount of time before delivery. These symptoms alone do not necessarily indicate that the baby has inhaled in the fluid by gasping in utero or after birth. After birth, rapid or labored breathing, cyanosis, slow heartbeat, a barrel-shaped chest or low Apgar score are all signs of the syndrome.Complications of MAS include pneumothorax and persistent pulmonary hypertension of the newborn.
Amnioinfusion, a method of thinning thick meconium that has passed into the amniotic fluid through pumping of sterile fluid into the amniotic fluid, has not shown a benefit in treating MAS .