Every parent-to-be hopes for an uncomplicated birth and a healthy baby. But some babies do face delivery room complications. One that may affect a newborn's health is meconium aspiration, also referred to as meconium aspiration syndrome (MAS). Although it can be serious, most cases of MAS are not.
MAS can happen before, during, or after labor and delivery when a newborn inhales (or aspirates) a mixture of meconium and amniotic fluid (the fluid in which the baby floats inside the amniotic sac). Meconium is the baby's first feces, or poop, which is sticky, thick, and dark green and is typically passed in the womb during early pregnancy and again in the first few days after birth.
The inhaled meconium can partially or completely block the baby's airways. Although air can flow past the meconium as the baby breathes in, the meconium becomes trapped in the airways when the baby breathes out. The meconium irritates the baby's airways and makes it difficult to breathe.
MAS can affect the baby's breathing in a number of ways, including chemical irritation to the lung tissue, airway obstruction by a meconium plug, infection, and the inactivation of surfactant by the meconium (surfactant is a natural substance that helps the lungs expand properly).
The severity of MAS depends on the amount of meconium the baby inhales as well as underlying conditions, such as infections within the uterus or postmaturity (when a baby is overdue, or more than 40 weeks gestational age). Generally, the more meconium a baby inhales, the more serious the condition.
Although 6% to 25% of newborns have meconium-stained amniotic fluid, only about 11% of them will have some degree of MAS.
Before a baby is born, fluid usually moves in and out of the trachea (the upper part of the airway) only. Meconium can be inhaled into the lungs if the baby gasps while still in the womb or during the initial gasping breaths after delivery. This gasping usually happens because a problem (such as an infection or compression of the umbilical cord) made it hard for the baby to get enough oxygen before birth.
MAS is often related to fetal stress. This can be caused by problems in the womb, such as infections, or by difficulties during the birth. A distressed baby may have hypoxia (decreased oxygen), which can make the baby's intestinal activity increase and cause relaxation of the anal sphincter (the muscular valve that controls the passage of feces out of the anus). This relaxation then moves meconium into the amniotic fluid that envelops the baby.
But meconium passage during labor and delivery isn't always associated with fetal distress. Sometimes, babies who aren't distressed during labor pass meconium before birth. In either case, a baby that gasps or inhales meconium can develop MAS.
Other risk factors for MAS include:
Prematurity is not a risk factor. In fact, MAS is rare in babies born before 34 weeks.
Before or at birth, the doctor will likely notice one or more symptoms of MAS, including:
If a baby is thought to have inhaled meconium, treatment will begin during delivery. If the baby has trouble breathing, the doctor will insert a laryngoscope into the trachea to remove any meconium. The doctor also will listen to the baby's lungs to check for sounds that are common with MAS.
The doctor might order tests, such as a blood test (called a blood gas analysis) that helps determine if the baby is getting enough oxygen and a chest X-ray that can show patches or streaks on the lungs that are found in babies with MAS.
Current guidelines say that if a newborn has inhaled meconium but is active, looks well, and has a strong heartbeat (>100 bpm), the delivery team can watch the baby for MAS symptoms (such as increased respiratory rate, grunting, or cyanosis), which usually appear within the first 24 hours.
For a newborn that has inhaled meconium and is not very active, has a lower heart rate (<100 bpm), is limp, and has poor muscle tone, the goal is to clear the airway as much as possible to decrease the amount of meconium the baby inhales. This is done by using an endotracheal tube (a plastic tube that's placed into the baby's windpipe through the mouth or nose) and applying suction as the tube is slowly removed. This allows suctioning of both the upper and lower airways. The doctor will continue trying to clear the airway until there's no meconium in the suctioned fluids.
Most babies with MAS improve within a few days or weeks, depending on the severity of the aspiration. Although a baby's rapid breathing may continue for days after the birth, there's usually no permanent lung damage. Some studies, however, suggest that babies born with MAS are at a higher risk for reactive airway disease (an asthma-like narrowing of the airways that can cause wheezing, coughing, and shortness of breath).
Babies with MAS may be sent to a special care nursery or a neonatal intensive care unit (NICU) to be closely watched for the next few days. Treatments might include:
Babies who have severe aspiration and need mechanical ventilation are at a higher risk for bronchopulmonary dysplasia, a lung condition that can be treated with medication or oxygen.
Another complication associated with MAS is a collapsed lung. Also known as pneumothorax, a collapsed lung is treated by reinflating the lung (inserting a tube between the ribs, allowing the lung to gradually re-expand).
Although rare, a small percentage of babies with severe MAS develop aspiration pneumonia. If this happens, the doctor may recommend advanced lung rescue therapy. Three therapies are used to treat aspiration pneumonia and severe forms of MAS:
If one of these therapies (or a combination of them) doesn't work, there is another alternative. Extra corporeal membrane oxygenation (ECMO) is a form of cardiopulmonary bypass, meaning that an artificial heart and lung will temporarily take over to supply blood flow to the baby's body. ECMO lowers the fatality rate for these severely distressed babies from 80% to 10%. Not all hospitals are ECMO centers, so babies that need ECMO might need to be moved to another hospital.
Babies with severe cases of MAS may come home from the hospital on oxygen. They may be more likely to have wheezing and lung infections during their first year, but lungs can regenerate new air sacs, so the long-term outlook for their lungs is excellent.
Severely affected babies are at risk for chronic lung disease and also may have developmental abnormalities and hearing loss. Babies diagnosed with MAS will be screened at the hospital for hearing problems or neurological damage.
Although very rare, severe cases of MAS can be fatal. But deaths from MAS have decreased greatly thanks to treatments such as suctioning and a reduction in the number of post-term births.
It's important for a pregnant woman to tell her doctor immediately if she sees meconium in the amniotic fluid when her water breaks, or if the fluid has dark green stains or streaks. Doctors also use a fetal monitor during labor to watch the baby's heart rate for any signs of fetal distress.
In some cases, doctors may recommend amnioinfusion (diluting the amniotic fluid with saline) to wash meconium out of the amniotic sac before the baby has a chance to inhale it at birth.
Although MAS is a frightening complication for parents to face during the birth of their child, most cases are not severe. Babies are monitored for fetal distress during labor, and doctors pay careful attention for any signs of meconium aspiration. If it does happen, treatment will begin immediately.
For most infants who have inhaled meconium, early treatment can prevent further complications and help reassure anxious new parents.
Reviewed by: Jay S. Greenspan, MD
Date reviewed: October 2014
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