Meconium is a thick, greenish substance that lines the lower intestines of the fetus. It’s made up of mucus, lanugo, epithelial cells, and amniotic fluid. In most cases, it will be your baby’s first bowel movement. Meconium is different from ordinary stool because it is sterile.
In ordinary circumstances, your baby will pass the meconium within the first few days after birth. However, sometimes the baby passes the meconium while still in the uterus. When that happens, it can have a serious impact on your baby’s health.
Meconium aspiration syndrome occurs when the baby expels the meconium while still in the uterus and then makes a reflexive gasping movement, drawing meconium-contaminated amniotic fluid into the lungs. In addition, a baby that has expelled meconium will be born covered in the meconium-stained amniotic fluid and may aspirate that fluid with its first breaths. The sticky meconium can block the airways, irritate the lung tissue, and impair the lungs’ ability to exchange oxygen efficiently after birth.
The baby expels meconium before delivery in up to 20% of births. Of those babies who expel meconium before delivery, up to 10% will suffer some degree of meconium aspiration syndrome. Most babies who prematurely expel meconium do not aspirate it and won’t suffer any adverse effects.
Causes Of Premature Release Of Meconium
Babies don’t produce meconium until about 35 weeks of gestational age. As they approach 40 weeks of gestational age, their bodies are maturing and getting ready to handle life outside the womb. That means their digestive tracts kick into gear and produce the meconium. It also means they start to have reflexive reactions, such as gasping.
In general, babies expel the meconium prematurely due to stress in the womb. Most commonly, that stress is caused by a shortage of oxygen. An oxygen shortage also causes the gasping reaction that pulls the meconium-stained amniotic fluid into the lungs. An oxygen shortage can happen when the placenta ages and loses efficiency, when the umbilical cord is compressed, as a result of a difficult or prolonged delivery, as a result of maternal health issues, or as a result of fetal health issues.
Meconium aspiration syndrome is most common in babies who are delivered at or after term. The placenta wears out over the course of 40 weeks and loses some of its ability to deliver enough oxygenated blood to the fetus. That can cause fetal stress and cause the baby to expel and aspirate meconium in the womb.
In addition, babies who remain in the womb past term have more developed reflexes and internal systems and are more likely to release meconium. Post-term babies are also larger and surrounded by less amniotic fluid, meaning the concentration of any meconium released into the womb is higher and more likely to result in meconium aspiration syndrome.
Umbilical Cord Compression
The umbilical cord is the baby’s lifeline. It carries vital nutrients and oxygen from the mother to the baby to nourish and support the baby in the womb. If the umbilical cord is compressed, the flow of nutrients and oxygen is diminished. That can cause the stress that leads to meconium release and aspiration.
Cord compression may occur simply as a result of the baby’s position in the womb. The cord may get trapped between the baby and the mother’s pelvis or the wall of the womb. Cord compression may also occur as the baby changes positions during delivery. Your doctor or midwife will try to make sure the cord stays as free as possible during delivery to avoid cord compression.
Difficult Or Prolonged Labor
Labor is stressful even if it’s relatively uncomplicated. A difficult or prolonged labor is even more stressful for both mother and baby. The baby has been in a warm, stable womb for its entire life and is suddenly squeezed by contractions and forced through the birth canal. That alone causes stress and the pressure of labor can also compress the umbilical cord. The longer and more difficult the labor, the more likely it is that the baby will become stressed enough to release meconium.
Labor can be difficult or prolonged for a variety of reasons. Most commonly, labor is difficult simply because the baby is too large to pass through the mother’s pelvis easily. In some cases, the baby may have macrosomia (high birth weight) due to maternal diabetes, maternal obesity, or certain genetic conditions. In other cases, the mother simply has a narrow pelvis.
Labor may also be difficult or prolonged if the baby is born in a breech position. Babies are typically born headfirst so that the arms are by the baby’s sides and can pass more easily through the birth canal. In a breech presentation, the baby is born feet-first. This makes delivery more difficult and can stress the baby.
Maternal Health Issues
A pregnant person’s health can have a serious impact on the baby. Sometimes, maternal health issues cause enough stress to cause the baby to expel meconium. If the mother has high blood pressure or diabetes, labor exacerbates these issues and stresses the mother’s body. That, in turn, stresses the baby.
Babies born to mothers who use tobacco or drugs (especially cocaine) during pregnancy can have a range of health issues, but they are particularly prone to meconium aspiration syndrome. They are more likely to experience distress in the womb and release meconium.
Fetal Health Issues
In some cases, the baby may experience distress in the womb because of health issues. For example, a baby that has an underdeveloped circulatory system or abnormally high blood pressure is more likely to release meconium in the womb. Fetal health issues don’t typically directly cause the release of meconium, but add to the stress of labor and make the release of meconium more likely.
Prevention of Meconium Aspiration Syndrome
The best way to prevent meconium aspiration syndrome is to avoid the release of meconium in the first place. That means minimizing the risk of fetal distress, which you can achieve by staying as healthy as possible during pregnancy. A healthy pregnancy involves eating the right foods, getting the proper amount of exercise, and avoiding tobacco, alcohol, and drug use.
Even in the healthiest pregnancies, however, fetal stress may be unavoidable. The causes of fetal stress during labor are varied, but attentive medical care can help identify fetal distress early and prevent meconium aspiration syndrome. When your water breaks, take a look at the fluid. If it’s greenish or brownish, it’s likely that the baby has released meconium.
Even if your amniotic fluid is clear of meconium when your water breaks, your doctor or midwife will pay close attention to your heart rate and to the baby’s heart rate. A sudden change in either can indicate fetal distress. If your pregnancy is high-risk, your doctor may perform certain tests to look for other indications of fetal stress.
Depending on the reasons for the fetal distress, the doctor or midwife may want to speed up the delivery to get the baby out before it releases meconium or suffers other adverse effects. In any event, the baby’s mouth and nose will be suctioned as soon as they’re accessible in order to remove any meconium and avoid aspiration.