We might think of amniotic fluid as pristine, clear water, but your growing baby was already making a mess. Old skin cells and hairs, which would become dust in the outside world, began to build up in the fluid. Unlike later in life, your baby cleaned up her own mess. As soon as she began swallowing, she removed the debris from the fluid. This sludge began to accumulate in her intestines. Called meconium, this dark-green tarry substance is a mixture of hair, cells, enzymes, blood, mucus, and other secretions. By the time of your baby’s birth, the meconium had filled most of her intestines. Meconium is sterile — very unlike the bacteria-filled stools that will follow.
Most babies pass the first meconium stool in the first 12 hours after birth. I love watching new dads trying to change a sticky meconium diaper. Often they end up with tarry meconium everywhere. Within a few days, the meconium stools give way to soft yellow-green breast milk stools or yellow-tan formula stools. If no meconium stool has been passed within the first 48 hours, the baby should be evaluated.
If a baby passes a meconium stool before birth, the amniotic fluid is stained and the baby is covered with meconium (reminiscent of the mess dads can make changing diapers). The baby is also likely to swallow the meconium, which sounds disgusting but doesn’t present a problem. The sterile meconium does not predispose to urinary tract infections, but meconium can cause significant problems if it is inhaled into the lungs.
This is called meconium aspiration.
If a baby makes it safely through the first breaths, the meconium staining becomes nothing more than a mess to be wiped off.
Some babies, about 7 to 20 percent, pass a meconium stool before they are born (Velaphi S. Vidyasagar D. Clinics in Perinatology. 33(1):29-42, v-vi, 2006 Mar). This is a common response to fetal distress. Stress, especially decreased oxygen to the baby, causes the sphincter muscles to relax and stool to be pushed out. (It is possible to “scare the poop” out of a baby even before they are born.) Non-stressed, healthy babies also sometimes pass stools before they are born. They are more likely to pass a stool before birth the longer they go past their due dates.
In only about 2 to 5 percent of babies born in meconium-stained amniotic fluid will some of the thick, tarry meconium be inhaled, plug the small airways, and thus cause respiratory distress.
Problems with meconium will be suspected if the amniotic fluid is stained when the bag of water breaks. Depending on the situation, the person caring for your child at the delivery may look at the vocal cords with a scope to see if any meconium has reached that area.
If aspiration has occurred, symptoms of respiratory distress may follow.
The course varies considerably. For some this is a mild problem; for others it is quite severe, even resulting in death or residual respiratory problems, such as wheezing or cough, for years.
It is diagnosed by observation and examination at the time of delivery, and in the nursery afterwards.
Meconium aspiration is first treated by trying to remove as much of the meconium as possible. How they are treated from there varies considerably depending on the condition of the child. Up to 30 percent of kids who develop meconium aspiration pneumonias need to go on mechanical ventilators.
Speedy delivery of distressed babies and suctioning the mouth and nose when the head has been delivered (before the expanding lungs take their first breath) can help prevent this meconium aspiration. Sometimes, more vigorous suctioning or even infusing extra amniotic fluid into the uterus before birth is needed.
Thick meconium; Particulate meconium, Inhaled stool.