When meconium is noticed in amniotic fluid during labour, it often initiates a cascade of interventions. A CTG machine will often be strapped onto the woman, reducing her ability to move and increasing her chance of having a c-section or instrumental birth. Time limits for labour may be tightened up further, resulting in induction or augmentation, which increases the chance of fetal distress and for first-time mothers, a c-section. As the baby is being born, they may be subjected to airway suctioning which can cause a vagal response (heart rate deceleration) and difficulties with breastfeeding. Once born, the baby is likely to have their umbilical cord cut prematurely and be given to a paediatrician who may also suction the baby's airways. In the first 24 hours after birth, the baby will be disturbed regularly to have their temperature, breathing and heart rate assessed. In some hospitals, the baby will be taken away from their mother to be observed in a nursery.

This is a lot of fuss for a bit of poop which in the vast majority of cases is not a problem. Indeed, many of the interventions implemented because of the meconium are more likely to cause complications than the meconium itself.

This post is mainly based on two journal articles: one by Unsworth & Vause [1] was published in an obstetric journal, and the other by Powell [2] published in a midwifery journal. Both articles agree that very little is known about meconium and whether it is a problem at all.

Meconium is a mixture of mostly water (70-80%) and a number of other interesting ingredients (amniotic fluid, intestinal epithelial cells, lanugo, etc.). Around 15-20% of babies are born with meconium stained amniotic fluid.

There are five reasons (theoretically) that a baby may open their bowels before birth:

• The digestive system has reached maturity and the intestine has begun working, ie, moving the meconium out (peristalsis). This is the most common reason  – 15-20% of term babies and 30-40% of post-term babies will have passed meconium before birth.

• The umbilical cord or head is being compressed (during labour), ie, a vagally mediated gastrointestinal peristalsis. This is a normal physiological response and can happen without fetal distress. It may be why a lot of babies pass meconium as their head is compressed during the last minutes of birth and then arrive with a trail of poop behind them.

• If the baby is in a breech position, compression of the abdomen as their bottom moves through the vagina usually squeezes out meconium.

• In cases of Intrahepatic cholestasis during pregnancy, the baby may pass thin meconium. This may be due to the increased movement of fluids through the baby's bowel caused by bile acids.

• Fetal distress resulting in hypoxia. However, the exact relationship between fetal distress and meconium stained fluid is uncertain. The theory is that intestinal ischaemia (lack of oxygen) relaxes the anal sphincter and increases gastrointestinal peristalsis. However, fetal distress can be present without meconium, and meconium can be present without fetal distress.

Bear in mind that these are theories without evidence to support them. Indeed, in 'animal models, ' the theory that hypoxia results in meconium is incorrect. There are also other theories about meconium in pregnancy—that the baby continually passes it and clears it—but I think this post is confusing enough without wading into them (see the key articles for further information).

Meconium alone cannot be relied on as an indication of...

Continue reading this article on Dr. Rachel Reed's website here.