The appearance of meconium-stained liquor (MSL) during labour is generally considered to be a sign of hypoxia and a predictor of poor fetal outcome. But is this always true?

Meconium-stained amniotic fluid is present in approximately 15% of live births (SCV 2021). Traditionally, MSL has been considered a sign of fetal distress due to hypoxia. However, it can also simply be a physiological response to a normally maturing gastrointestinal tract, causing no ill effects on the fetus at all (Skelly et al. 2022).

Why is Meconium Sometimes Passed Before Birth?

Reed (2023) suggests that there are five reasons why the fetus may pass meconium before birth:

1. Their digestive system has reached maturity, so the intestine has begun working and moving the meconium out. This is the most common reason.
2. Their cord or head is being compressed during labour, causing a vagally mediated gastrointestinal peristalsis.
3. Fetal distress resulting in hypoxia. Although the exact relationship between fetal distress and meconium-stained liquor is uncertain, it’s thought that lack of oxygen and intestinal ischaemia relax the anal sphincter and increase gastrointestinal peristalsis, resulting in the passage of meconium.
4. The fetus is in a breech position, which can cause compression of the abdomen, and, consequently, meconium to be squeezed out.
5. Intrahepatic cholestasis of pregnancy, which can cause increased movement of fluids through the fetus’s bowel and lead to the passage of thin meconium.

It’s worth pointing out that fetal distress can be present without the presence of meconium, and meconium can be present without fetal distress (Reed 2023).

Is the Presence of Meconium-Stained Liquor Always Dangerous?

Addisu et al. (2018) state that there are two classifications of MSL: non-significant and significant.

1. Non-significant MSL is defined as a thin yellow or greenish-tinged fluid, containing non-particulate meconium.
2. Significant MSL is defined as amniotic fluid containing lumps of meconium, or dark green or black amniotic fluid that is thick and tenacious.

Additional indicators of a potentially adverse neonatal outcome include MSL associated with an abnormal cardiotocograph (CTG), which is more likely to result in a caesarean birth and potential neonatal complications (Priyadharshini 2013).

That said, it’s always important to consider the whole clinical picture before deciding if the presence of meconium is a significant finding or not.

Whilst it’s true that the presence of meconium in the amniotic fluid can be a potentially serious sign of fetal compromise associated with poor perinatal outcome (Vaghela et al. 2014), it’s also true that most babies who are born in poor condition do not have meconium-stained liquor and most babies with meconium-stained liquor are born in good condition (Reed 2023).

In a global sense, MSL is still considered to be a marker for adverse perinatal outcomes. Whilst the passage of meconium alone is rarely a sign of significant fetal hypoxia or acidosis, meconium in the presence of an abnormal fetal heart rate (FHR) pattern should always be investigated further.

As Qadir et al. (2016) suggest, the presence of thick meconium is associated with an increase in perinatal morbidity and mortality, and its presence should never be overlooked.

Risk Factors for Meconium Aspiration Syndrome

Meconium aspiration syndrome (MAS) is a potentially-fatal condition that can occur when the infant accidentally inhales meconium during delivery (Skelly et al. 2022).

MAS is estimated to occur in 5% of births where meconium-sained liquor is present (SCV 2021).

Overall, MAS is known to have a higher incidence with:

• Increase in gestational age
• Birth weight > 2.5 kgs
• Caesarean births.

(Hirani et al. 2015)

The Debate About Intervention

Whilst each hospital will have its own documented policies on the management of meconium-stained liquor, Reed (2023) urges all practitioners to consider the holistic picture and suggests the following practical steps that might help lower the risk of meconium aspiration syndrome:

• Avoid artificial rupture of the membranes (ARM) during labour. If there is meconium present, it will remain well-diluted, and the amniotic fluid will protect the baby from compression during contractions.
• Ensure that the mother knows meconium is a variation and not necessarily a complication. A post-date baby with old meconium is very different from a 38-week baby with thick, fresh meconium.
• Avoid any interventions that are associated with fetal distress, such as ARM, the use of syntocinon/pitocin, or directed pushing.

Safer Care Victoria (2021) also comment on the following areas of uncertainty in clinical practice, suggesting that:

• There is no evidence that management should be based on the consistency of meconium.
• There is no evidence that techniques used to inhibit gasping after birth can be effective in reducing the incidence of MAS.

Ongoing Care of Infants Born Through Meconium-Stained Liquor

Following birth, infants born through MSL may require ongoing care.

• The infant may require continued resuscitation, depending on their condition
• If the infant develops apnoea or respiratory distress, they will require intubation and tracheal suctioning prior to assisted ventilation
• Once resuscitation is complete, aspiration of the stomach is recommended
• The infant may require admission to special care nursery for observation if:
  • There is meconium below the cords
  • They are experiencing ongoing respiratory distress, or require oxygen
  • There is need for active resuscitation involving CPR or prolonged IPPV.

(SCV 2021)

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