Meconium is a newborn's first feces, which is typically passed in the first few days after birth. Although it doesn't have any bacteria or odor, meconium can cause problems if a baby passes it while still in the uterus, where it will mix with amniotic fluid, and inhales (aspirates) the mixture before, during, or just after birth. This is called meconium aspiration, and it usually happens in babies born on time or post-term — after 42 weeks — as opposed to premature infants.
Passage of meconium before birth can be triggered by different stresses to the fetus. Usually this stress results from normal labor contractions, but sometimes it's due to other causes, such as infection and poor blood or low oxygen flow to the fetus.
When meconium gets into the mother's amniotic fluid, it's called meconium staining, and the amniotic fluid may have a greenish color or streaks of green. Meconium can be seen in the amniotic fluid in about 12 percent of all deliveries.
If meconium's found in the amniotic fluid, doctors take special precautions to prevent the baby from breathing it in. Most babies who are treated with these precautions breathe just fine and never develop further problems. However, a small group of these infants can become quite sick, even when all precautions are taken.
Meconium particles in the amniotic fluid can block small airways and prevent a baby from breathing properly, causing respiratory distress. If this occurs, some babies may need the help of a mechanical breathing machine. A baby who has inhaled meconium may also develop an infection, which can cause pneumonia.
Furthermore, some babies with meconium aspiration go on to develop a condition called pulmonary hypertension. Pulmonary hypertension decreases the flow of blood into the lungs, where it normally picks up oxygen. Instead, blood bypasses the lungs, and very little oxygen gets to the baby. The condition often improves within a few days, although severe meconium aspiration and pulmonary hypertension may be fatal in a very small percentage of babies.
Risk factors for meconium aspiration include:
Each baby may experience symptoms of meconium aspiration differently, but the following are the most common signs:
Exposure to meconium in the amniotic fluid for a long time may cause yellowed skin and nails.
The presence of meconium in a mother's amniotic fluid is key to diagnosing meconium aspiration. If meconium aspiration is suspected, your doctor may examine your baby's vocal cords for meconium staining through a procedure called laryngoscopy. The doctor may also listen to your baby's chest with a stethoscope to check for sounds of abnormal breathing. An X-ray of your baby's chest may also help diagnose the condition.
Treatments for meconium aspiration depend on the amount and thickness of the meconium, length of time your baby was exposed to it and the severity of the respiratory problems your baby is experiencing.
If a mother's amniotic fluid appears to have meconium, a technique called amnioinfusion may be used during labor. This procedure involves inserting a small tube into the uterus through the vagina to infuse the amniotic fluid with sterile fluid, which may help to dilute the meconium.
Other treatments performed at delivery may include:
Reviewed by health care specialists at UCSF Benioff Children's Hospital.