Meconium aspiration

Up to 15% of babies pass meconium during delivery, which is dangerous if aspirated. Unfortunately, birth asphyxia provokes vigorous breathing movements in the foetus which contributes to aspiration of meconium into the respiratory tree.

Meconium may act as a ball valve - allowing air in but not out. This results in a radiographic appearance of patchy consolidation interspersed with areas of overinflation.

Meconium is also acidic and acts as an irritant, resulting in a chemical pnemonitis. Bacteria may cause superinfection.

Meconium passage in a preterm infant is always abnormal, and should raise suspicion of Listeria infection.

NICE guidance states (1):

Presence of meconium in labour

• when assessing risk at any time during labour, be aware that the presence of meconium:
  • can indicate possible fetal compromise, and
  • may lead to complications, such as meconium aspiration syndrome
    
    
• consider the character of the meconium as part of the overall clinical assessment, in conjunction with other antenatal or intrapartum risk factors, and discuss the option of CTG (cardiotography) monitoring with the woman. Recognise that the type of monitoring method used is the woman's choice, and support her decision
  
  
• be aware that meconium is more common post-term, but should still trigger a full risk assessment and discussion with the woman about the option of CTG monitoring
  • means that continuous cardiotocography monitoring may be advised (2)
  • be aware that meconium is more common after full term but should still trigger a full risk assessment and discussion with the woman about the option of transfer to obstetric-led care (2)

Reference:

1. NICE (December 2022). Fetal monitoring in labour
2. NICE (September 2023). Intrapartum care