Meconium is a dark green liquid normally passed by the newborn baby, containing mucus, bile and epithelial cells.
However, in some cases the meconium is passed when the baby is still in the womb, staining the amniotic fluid. This can vary from light to heavy staining. It is considered significant if dark green or black, with a thick, tenacious appearance.
Components of the meconium, especially the bile salts and enzymes, can cause serious complications if they are inhaled by the fetus at any stage of labour. This can result in meconium aspiration syndrome (MAS). There are several pathological mechanisms participating in MAS, particularly airway obstruction, surfactant dysfunction, inflammation, lung oedema, pulmonary vasoconstriction and bronchoconstriction.
Meconium staining often occurs in conjunction with other causes of fetal distress. It is rare in babies born at <34 weeks of gestation.
The figure quoted for infants born with meconium-stained liquor in the industrialised world is 8-25% of births after 34 weeks of gestation. MAS occurs in around 1-3% of live births.
Deliveries complicated with meconium-stained amniotic fluid are associated with additional adverse pregnancy outcomes (eg, increased rates of labour dystocia, delivery by caesarean section and fetal distress).
Risk factors include:
- Placental insufficiency.
- Maternal hypertension and pre-eclampsia.
- Cocaine abuse.
- Increased maternal age.
Meconium-stained amniotic fluid is really worrisome from both the obstetrician's and the paediatrician's point of view, as it increases the caesarean rates, and causes birth asphyxia, MAS and an increase in neonatal intensive care unit admissions.
These recommendations are from the National Institute for Health and Care Excellence (NICE), 2014.
- If significant meconium staining is noted in labour, there should be continuous electronic fetal monitoring.
- This is defined as dark green or black amniotic fluid that is thick or tenacious, or any amniotic fluid that contains lumps of meconium.
- Transfer mother to obstetric-led care, if it is safe to do so and delivery is not imminent.
- If there are signs of fetal distress, a fetal blood sample should be obtained. If pH is <7.21, there should be emergency delivery.
- Ensure that the advanced resuscitation unit and appropriately trained staff are available.
- There should be no suction prior to delivery.
At delivery - healthy neonate
- If the baby is in good condition (Apgar score >5, based on colour, tone, heart rate and breathing), there should be no suction.
- The baby should be observed for signs of respiratory distress in the first hour of life, in the second hour and then two-hourly until 12 hours old.
- If there is blood or if there are lumps of meconium in the oropharynx, suction should be used in the upper airways.
- Endotracheal intubation at birth in otherwise healthy, term meconium-stained babies, is no longer recommended.
At delivery - sick neonate
See the separate article Meconium Aspiration for further information.
Infant respiratory distress syndrome
- Respiratory distress that usually occurs within four hours of birth and becomes persistently worse for 48 to 72 hours is known as infant respiratory distress syndrome. If not fatal, it resolves by 72 hours.
- A deficiency of surfactant produces high alveolar surface tension. The baby must re-inflate the collapsed alveoli with every breath. Thus, every breath takes a lot of effort for relatively poor expansion.
- Surfactant replacement therapy has shortened the duration of the disease and significantly reduced mortality.It is treated with administration of synthetic or animal surfactant.
Persistent pulmonary hypertension of the newborn
- Babies may have persistent pulmonary hypertension of the newborn, as a consequence.
- This occurs where the fetal circulation persists with blood being shunted away from the lungs through the foramen ovale and a patent ductus arteriosus.
- It is a consequence of raised pulmonary vascular resistance. Clinical features include cyanosis, tachypnoea and the murmur of patent ductus arteriosus.
- Supportive measures, including ventilation.
- Prostacyclin infusion.
- Extracorporeal membrane oxygenation (ECMO).
- Several promising therapeutic modalities for this condition: these include oxygen supplementation, mechanical ventilation, nitric oxide, phosphodiesterase enzyme inhibitors, endothelin receptor antagonists, and ECMO.
Chronic lung disease
- Children with meconium aspiration may develop chronic lung disease as a result of intense pulmonary intervention.
- Infants with meconium aspiration have a slightly increased incidence of infections in the first year of life because the lungs are still in recovery.
- Up to 10% of cases of meconium staining develop MAS.
- Nearly all infants with MAS have complete recovery of pulmonary function.
- Initial hypoxic events may cause the infant to have long-term neurological problems, including seizures, general learning disability and cerebral palsy.
Elective induction of labour for pregnancies at or beyond 41 weeks has been shown to be associated with significant reduction in the incidence of MAS and fewer perinatal deaths compared to expectant management.
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