Meconium is stool produced in the digestive system of a fetus. It is dark green and odorless. Before and during birth, the newborn excretes meconium, and it mixes with the amniotic fluid. In some cases, this process exposes the infant to meconium amniotic fluid fumes, causing meconium aspiration syndrome (MAS). MAS blocks the airways and reduces the surface area of the lungs, leading to depressed inhalation of oxygen.
During pregnancy, the fetus ingests materials through the umbilical cord that links him or her to the mother. Additionally, water, bile, amniotic fluid, and mucus enter the fetus’ digestive system. Studies show even lanugo, the soft hair on the fetus' skin, can get into the system. This mixture forms meconium.
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Microbiology research indicates meconium is not sterile, as previously thought. Samples contain bacterial communities developed enough to fall into two categories: enteric bacteria and lactic acid-producing bacteria. Generally, these bacteria are essential to physiological processes such as digestion. If they reach the lungs of an infant with MAS, however, they can interfere with the aspiration process and lead to health complications.
When the fetus passes stool and it comes into contact with the amniotic fluid, the baby can inhale the mixture. The passing of meconium is an indication that the baby is ready for birth. This transition exposes the baby to labor stress and, consequentially, MAS. Factors that increase the risk include maternal diabetes or high blood pressure, late birth, prolonged labor, deprivation of sufficient oxygen to the fetus while in the uterus, and induced labor.
In a 42-week pregnancy, the baby’s digestive system is already mature and ready to excrete meconium. Normal contractions can exert pressure on the baby, leading to MAS. Additionally, during vaginal births, there can be head entrapment, cord prolapse, or cord entanglement. These events prolong labor and raise the risk of inhalation. However, emergency measures can limit the extent of aspiration and therefore the development of MAS.
Experts estimate seven to 22% of all deliveries are affected by meconium amniotic fluid aspirations. Reports indicate in 42-week pregnancy deliveries, the percentage of MAS surges to 30%. Hormone motilin is responsible for the syndrome, as it induces defecation, bowel peristalsis, and maturity of the innervation in the intestinal tract is associated with vagal nerve stimulation during birth.
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Too much or too little amniotic fluid, uterine growths such as fibroids, and premature deliveries can cause breech births, wherein the fetus fails to turn so the head is towards the vaginal canal. Although medical practitioners can correct breech positions in prenatal care through the external cephalic version (EVC) therapy, cesarean births are the more common solution. However, since the fetus may be exposed to the product that causes MAS before birth, it is still possible of c-section-born babies to develop the condition.
There is one sure sign that a fetus has passed the meconium in the uterus: when the water breaks, a residue is visible in the liquid. If the residue is brownish, the meconium is aged, and the fetus has been in distress for longer; if the residue is dark green and thick, this means that the meconium passed recently and stress is just beginning. At this point, the mother should immediately notify the doctor to ensure timely intervention.
Before delivery, it is not easy to tell whether a baby has inhaled the meconium amniotic fluid, though a slow heart rate can indicate the issue. When the medical practitioner first holds the newborn, however, the following signs can indicate MAS:
The doctor will then confirm the diagnosis using a chest x-ray and blood tests, looking for oxygen or carbon dioxide.
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In itself, meconium has minimal impact on the health of a child. However, lack of treatment can lead to inflammation of the respiratory system and increased chance of asthma in adulthood. Further, oxygen deprivation arising from the syndrome can cause persistent pulmonary hypertension of the newborn (PPHN), stroke, or cerebral palsy, due to brain damage. As long as medical practitioners are watching for the signs of MAS and treating symptoms promptly, these complications can be largely avoided.
Although some mild cases may not require intervention, it is always advisable to treat meconium aspiration syndrome. When the doctor confirms the diagnosis, he or she can administer a transcervical amnio-infusion using warmed conventional saline. Other treatments include chest physiotherapy, systemic steroid treatment, administration of surfactants, lungs and airway suction, assisted breathing through ventilators, and antibiotics. If the situation is life-threatening, the baby may need to spend time in the neonatal intensive care unit.
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