Meconium

Question 1

What % of fetuses beyond 42 weeks pass meconium?

Answer 1

45%

Question 2

What the physiological mechanism for physiological meconium passage?

Answer 2

Parasympathetic NS stimulation increases gut motility.
Vagal response to head compression in labour can cause meconium passage. (Therefore uncommon in first stage of labour).

Must always be light and in absence of risk factors (placental insufficiency, hypoxia, infection) to be considered physiological.

Question 3

List the causes of meconium passage

Answer 3

• Physiological
• Fetal hypoxia
• Fetal gut abnormality e.g. gastroschisis
• Maternal obstetric cholestasis esp if bile acids >40.
• Listeria: preterm and rare.
• Infection

Question 4

What are the consequences of meconium passage?

Answer 4

Increased risk of cerebral palsy:

• 2 x more common at term.
• Especially preterm: 40% risk of CP with MSAF vs 10% risk of CP if clear liquor.

Neonatal meconium aspiration syndrome (chemical pneumonitis, persistent pulmonary hypertension)

Question 5

How does fetal hypoxia increase the risk of neonatal meconium aspiration syndrome?

Answer 5

Hypoxia increases the risk of fetal gasping in utero (associated with terminal apnoea) and increases risk of aspiration.