Even though fetuses do not eat, their intestines contain a sterile substance called meconium.
Fetuses sometimes pass meconium into the amniotic fluid before birth, either normally or in response to stress, such as a lack of oxygen.
Stress may cause fetuses to gasp reflexively, thus inhaling amniotic fluid containing meconium into their lungs.
Affected newborns have bluish skin and/or lips, rapid and labored breathing, and can make a grunting sound when breathing out.
The diagnosis is based on seeing meconium in the amniotic fluid at birth, along with trouble breathing and abnormal chest x-ray results.
Affected newborns require supplemental oxygen and may require assistance with a ventilator.
Most affected newborns survive, but the syndrome can be fatal if severe.
(See also Overview of General Problems in Newborns.)
Meconium is the dark green, sterile fecal material that is produced in the intestine before birth. Meconium is usually passed after birth when newborns start to feed, but sometimes it is passed into the amniotic fluid before or around the time of birth. Passage of meconium may be normal before birth, particularly just before or after the due date. But sometimes meconium passage occurs in response to stress, such as by an infection or by an inadequate level of oxygen in the blood. Although meconium passage may be normal in a term or postmature fetus, it is never normal for there to be meconium noted at the delivery of a premature baby. Meconium passage in a premature baby most often means the baby developed an infection while in the womb.
Meconium aspiration syndrome occurs when stress (such as infection or low oxygen levels) causes the fetus to take forceful gasps, so that the amniotic fluid containing meconium is breathed (aspirated) in and deposited into the lungs. After delivery, the aspirated meconium may block the newborn's airways and cause regions of the lungs to collapse. Sometimes airways are only partially blocked, allowing air to reach the parts of the lung beyond the blockage but preventing it from being breathed out. Thus, the involved lung may become over-expanded. When a portion of the lung continues to over-expand, it can rupture and then collapse the lung. Air may then accumulate within the chest cavity around the lung (pneumothorax).
Meconium aspirated into the lungs also causes inflammation of the lungs (pneumonitis) and increases the risk of lung infection.
Newborns with meconium aspiration syndrome are also at increased risk of persistent pulmonary hypertension of the newborn.
Affected newborns have respiratory distress, in which they breathe rapidly, draw in their lower chest wall while breathing in, and grunt during breathing out. Their skin and/or lips may be bluish (a condition called cyanosis) if the blood levels of oxygen are reduced. They may also develop low blood pressure. The newborn's umbilical cord, nail beds, or skin may be covered in meconium, giving them a greenish yellow color.
Doctors base the diagnosis of meconium aspiration syndrome on the presence of meconium in the amniotic fluid at the time of birth, respiratory distress, and abnormal chest x-ray results.
Cultures of blood may be done to look for certain kinds of bacteria.
Most newborns with meconium aspiration syndrome have an excellent prognosis. However, occasionally, if the disorder is severe, especially if it leads to persistent pulmonary hypertension of the newborn, it can be fatal. Newborns with meconium aspiration syndrome may be at greater risk of asthma later in life.
Any problem that stressed the newborn and caused meconium passage can affect prognosis.
Doctors always used to do suctioning whenever they saw meconium in the amniotic fluid or in the newborn's mouth, but this has not been shown to help. However, if the newborn's airway seems blocked by meconium, doctors try to suction it out.
Newborns who have trouble breathing after delivery may need to have a breathing tube placed in their windpipe and be placed on a ventilator (a machine that helps air get in and out of the lungs), or they may be put on continuous positive airway pressure (CPAP). CPAP allows newborns to breathe on their own while being given slightly pressurized air, with or without extra oxygen, through prongs placed in the nostrils. Newborns are admitted to the neonatal intensive care unit (NICU) if necessary.
Newborns on a ventilator may be given synthetic surfactant (a substance that coats the inside of the air sacs and allows the air sacs of the lungs to remain open) and are observed closely for serious complications, such as pneumothorax or persistent pulmonary hypertension of the newborn.
Newborns may be treated with antibiotics given by vein if a bacterial infection is thought to be what caused the fetus distress before birth.