Meconium-stained liquor

Meconium is a dark green sticky liquid normally passed by the newborn baby as its first faeces, containing mucus, bile and epithelial cells.

However, in some cases the meconium is passed while in utero, staining the amniotic fluid. This staining can vary from light to heavy.

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, including antenatal infection/inflammation and activation of the inflammatory cascade, mechanical airway obstruction, inactivation of surfactant and persistent pulmonary hypertension.¹

Meconium staining often occurs in conjunction with other causes of fetal distress. It is rare in babies born at <34 weeks of gestation.

Epidemiologia

Meconium-stained liquor occurs in about 12-20% of all deliveries and but about 40% of post-term deliveries.²

Deliveries complicated with meconium-stained amniotic fluid are associated with increased frequency of operative delivery, birth asphyxia, neonatal sepsis, and neonatal intensive care unit admissions compared to clear amniotic fluid.³

I fattori di rischio includono:

• Placental insufficiency.

• Maternal hypertension and pre-eclampsia.

• Oligoidramnios.

• Maternal drugs including cocaine.

• Increased maternal age.⁴

• Peripartum infection.

• Prolonged labour.⁴

These recommendations are from the National Institute for Health and Care Excellence (NICE) guidance in 2023.

Intrapartum⁵

• 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), suction does not reduce the risks of meconium aspiration syndrome.⁶

• 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 babies born with meconium-stained liquor, is not recommended.

At delivery - sick neonate

Vedi il Aspirazione di meconio article for further information.

Infant respiratory distress syndrome⁷

• Respiratory distress occurs in less than 10% of babies born with meconium-stained liquor.

• Respiratory distress that occurs within four hours of birth and becomes persistently worse for 48 to 72 hours is known as infant respiratory distress syndrome. It usually resolves within 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 dotto arterioso pervio.

• It is a consequence of raised pulmonary vascular resistance. Clinical features include cyanosis, tachypnoea and the murmur of patent ductus arteriosus.

Trattamento⁸
Questo include:

• Supportive measures, including ventilation.

• Prostacyclin infusion.

• Extracorporeal membrane oxygenation (ECMO).

• Inhaled nitric oxide (iNO), which is well documented for treatment of PPHN, but 30% fail to respond.

• Other current treatment options - these could be sildenafil, milrinone, prostaglandin analogues and bosentan.

Malattia polmonare cronica

• 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.

• Around 2% to 10% of babies born through amniotic fluid stained with meconium develop meconium aspiration syndrome (MAS).⁹

• The mortality associated with meconium aspiration syndrome in the United States is around 1.2% and is higher in LEDCs.¹⁰

• Late term fetuses have higher risk of developing respiratory complications.¹¹

• 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 attacchi, general learning disability e paralisi cerebrale.

Elective induction of labour for pregnancies at or beyond 41 weeks but before 42 weeks may be beneficial in preventing meconium staining and aspiration but is associated with several other adverse outcomes.¹²