Meconium is a newborn baby's first bowel movement, and is the substance that the baby will excrete.
The meconium is thick, sticky and tar-like, and is dark green to black in colour. It is usually odourless and is sterile.
Meconium lines the baby's intestines while it is developing in the womb, and is made up of different waste products. These include cells from the wall of the bowel, amniotic fluid, mucus, water and bile pigment.
A baby will normally pass meconium a few hours or days after birth, although some babies may excrete meconium during labour or birth.
This is evident if the woman's amniotic fluid is tinged green, and is acknowledged as a sign that the baby is in distress. Therefore, the baby's condition will be carefully monitored if meconium is present.
The greatest risk from meconium is the baby inhaling the substance during delivery or with its first breath. If this happens, the baby is at risk from developing meconium aspiration syndrome (MAS). Around one third of babies who develop MAS will require help with breathing, and severe cases will need to be treated in the neonatal intensive care unit.
To minimise the risk of inhalation and MAS, doctors will suction as much of the meconium away from the baby during labour or birth. However, if inhalation occurs and MAS does develop, most babies will show improvement after a few days or weeks, depending on the severity of the condition. There is usually no permanent lung damage..