Meconium is the initial substance present in the intestines of the developing fetus and constitutes the first bowel movement of the newborn. Meconium can be green, brown, or yellow. Term healthy neonates pass meconium between 24 to 48 hours following birth. Preterm infants typically exhibit delayed passage.
The presence of meconium-stained amniotic fluid is about 12-20% of deliveries and is much higher in post-dated births (up to 40%). In-utero passage of meconium may indicate normal gastrointestinal maturation or more concerningly it may be a sign of acute or chronic fetal hypoxia. Some of the conditions associated with meconium passage in-utero include placental insufficiency, preeclampsia, oligohydramnios, peripartum infections, and certain maternal drugs such as cocaine. Babies born through a meconium-stained amniotic fluid are at higher risk of development of adverse events such as perinatal asphyxia and respiratory distress. The accidental inhalation of meconium in-utero or during delivery can result in an adverse event for the infant, which is known as meconium aspiration syndrome. This complication happens in about 3-9% of the babies delivered with meconium-stained amniotic fluid. To reduce the risk of adverse consequences related to meconium-stained amniotic fluid, the American College of Obstetricians and Gynecologists 2014 guidelines recommend induction of labor at or after 42 weeks. Similarly, induction of labor is to be considered between 41- 42 weeks of gestation. In-utero passage of meconium before 32 weeks of gestation is rare, and in preterm babies, meconium-stained amniotic fluid may indicate chorioamnionitis, fetal sepsis (e.g., listeriosis) or in-utero cord compression.
The passage of meconium within 24-48 hours after birth indicates that the intestines of the newborn are intact and patent. This assessment is important for the initial newborn examination. Failure to pass meconium beyond 48 hours in term neonates may indicate disease or obstruction of the infant's bowel. The diagnostic differential for the delayed passage of meconium includes Hirschsprung disease, meconium plug syndrome, meconium ileus, anorectal malformations, small left colon syndrome, and intestinal atresias. Hypothyroidism, sepsis, and electrolyte abnormalities (hypercalcemia, hypokalemia), and maternal medications (magnesium sulfate, illicit drugs) can also delay the passage of meconium.
In the event of the rupture of the fetal membranes, the nurse should assess the color of the amniotic fluid. Amniotic fluid should be clear, or straw tinged with small vernix particles in the fluid. Brown or green staining of the fluid indicates the passage of meconium. Because the fetus swallows amniotic fluid in utero, meconium can be present in the infant's oropharynx at delivery. During delivery, if meconium-stained amniotic fluid is noted, a neonatal resuscitation team should be promptly involved.
Traditionally, during labor, if meconium-stained amniotic fluid is encountered, an intrapartum suctioning of airways was done. Latest guidelines recommend changing these practices quoting that these procedures are of unknown benefit and may be even harmful. In the updated 2015 American Heart Association/American Academy of Pediatrics guidelines (AHA/AAP), routine intrapartum suctioning of the airways before the delivery of the shoulders is not recommended.
If the infant is vigorous with good muscle tone and respiratory efforts, further newborn care could be provided in the delivery room. Routine suctioning of the meconium-stained fluid from the oropharynx is not recommended in these infants. However, if the airway is obstructed, then the airway clearance with suctioning of the meconium is recommended. Close monitoring in the newborn nursery is warranted.
If the infant is not vigorous with poor neurological tone, insufficient breathing efforts, and bradycardia (heart rate <100 beats/minute), routine postnatal suctioning of the airways was widely practiced in the past to decrease the possibility of development of meconium aspiration syndrome. The 2015 AHA/AAP guidelines do not recommend this practice and rather recommend immediate appropriate management to support ventilation and oxygenation, such as commencing positive pressure ventilation. Interventions such as endotracheal intubation for positive pressure ventilation may be required in severe instances, and a prompt transfer to the neonatal intensive care unit for further management may be needed. Airway clearance with suctioning of the meconium is recommended if the airway is obstructed. The 2015 AHA/AAP guidelines emphasize on following the same resuscitation steps for infants with a meconium-stained amniotic fluid similar to those infants with clear fluid.
During labor, the assessment of the amniotic fluid color can determine if the infant is at risk for amniotic inhalation upon birth. If the meconium-stained amniotic fluid is noted, a neonatal resuscitation team should be involved. In places with limited perinatal resources, an amnioinfusion could be tried, but the benefits of this procedure are unclear. Latest guidelines emphasize on following the same resuscitation measures for infants with a meconium-stained amniotic fluid similar to those infants with clear fluid. The assessment of respirations, color, and signs of respiratory distress (grunting, nasal flaring, intercostal retractions, and tachypnea) are necessary after birth. Assessment for passage of meconium, which usually occurs during the first twenty-four hours of life, is part of the initial newborn examination and indicates an unobstructed gastrointestinal tract with a patent anus.
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