Meconium Aspiration Syndrome (MAS)

Breathing is very different in utero for your baby as he relies on the placenta for his oxygen exchange. Amniotic fluid even fills his lungs until he arrives and takes his first real breath. But sometimes during labor and delivery or while he’s still in the womb, an extra substance called meconium can slip into his airways, causing irritation and breathing issues.

Fortunately, this condition, which is called meconium aspiration syndrome or MAS, is often quickly diagnosed and treated successfully. Read on for more about MAS, including the symptoms and ways to prevent it.

What is meconium?

Meconium is a thick, dark green substance that’s considered your baby’s first poop. In most cases, you’ll see this greenish-black goo when you change your baby’s early diapers.

Until then, meconium resides in an infant’s intestines. And while it looks rather gross, it’s supposed to appear sticky and tar-like since this early stool is a mix of waste products such as cells, proteins and bile.

What is meconium aspiration syndrome (MAS)? 

When an infant breathes in a mixture of meconium along with the amniotic fluid that’s already present in the lungs, meconium aspiration syndrome can develop. MAS occurs when a baby has trouble breathing because of the presence of meconium. Exposure to it can happen while your baby is still in the womb or during or after delivery.

As for how common it is to have meconium in amniotic fluid, the rate is about 5 to 10 percent in normal pregnancies. And fortunately, only half of the babies with meconium in their fluid will go on to have breathing problems and even fewer (about 5 percent) will develop a case of MAS.

What causes meconium aspiration syndrome?

Meconium aspiration syndrome can sometimes occur when a baby is under stress due to low oxygen or an infection either in utero or during delivery. A baby may release meconium due to potential stressors like:

• Long labor. A tough, extended labor and delivery may up the risk of passing meconium.
• Overdue baby. Another factor is a longer-than-usual stay in the womb (more than 40 weeks). 
• Maternal health issues. If you have diabetes, high blood pressure or you’ve smoked or used drugs during pregnancy, meconium in the amniotic fluid is more likely.

If your baby releases meconium and then gasps, he may inhale amniotic fluid along with meconium.

What are symptoms of meconium aspiration syndrome?

The doctor and nurses on your delivery team will keep close tabs on your baby during labor and delivery, especially if you have one of the potential risk factors listed above. If your baby inhales meconium, these common MAS symptoms may occur before or after birth: 

• Fetal distress. Breathing trouble such as rapid breathing or grunting while inhaling, low blood pressure or a slowed heart rate could point to meconium in the lungs.
• Meconium staining. This means the amniotic fluid has a greenish hue to it, or the meconium could temporarily tint your baby’s skin, nails or umbilical cord.
• Bluish skin or limpness. Appearing limp and unresponsive or with bluish skin or lips are other possible symptoms.

How is meconium aspiration syndrome diagnosed?

Meconium aspiration syndrome diagnosis is most accurately made by using a laryngoscope to find meconium staining on the vocal cords. Fetal monitoring that detects a slow heart rate or the presence of meconium in the amniotic fluid can also signal a potential case of MAS.

Other diagnostics include listening to the baby’s chest for hoarse, rough breathing and a chest X-ray, which can show streaks on the lungs. And additional tests can rule out conditions with similar symptoms such as pneumonia. 

How is meconium aspiration syndrome treated?

Try not to worry too much about MAS as most babies get better in a matter of days or weeks, depending on how severe the case is. While suctioning a baby’s airways used to be standard care, it’s not clear how much this actually helps prevent MAS. Still, the doctor may attempt it, as well as some of these other treatment options:

• Warm and dry care. A special care nursery or NICU team will work to stimulate your baby by tapping on his chest and use a warmer to keep his temperature stable.
• Breathing mask. To help your baby get more air, faster, he may wear an oxygen mask to inflate his lungs.
• Antibiotics or an IV. If an infection caused the fetal distress, antibiotics can help, and if breathing issues prevent nursing or bottle feeding, IV nutrition is an option. 

In more severe cases, a baby may need a breathing tube, a ventilator or CPAP machine (continuous positive airway pressure) to aid breathing. Doctors can also administer what's called an artificial surfactant to help keep the lungs' air sacs open.

Can you prevent meconium aspiration? 

The best way to prevent meconium aspiration is to stay as healthy as you can during pregnancy and keep all of your prenatal care appointments. By sticking to this important schedule, you can update your doctor if you notice anything unusual — and get any necessary testing done right away. 

For example, if your water breaks and you see greenish-brown stains or streaks in the fluid, call the doctor ASAP. And if your due date comes and goes with no baby in sight, your doctor may recommend labor induction, which may help stave off a case of MAS.

What complications are associated with meconium aspiration?

Thankfully, most infants with meconium aspiration syndrome can recover quickly and won’t experience long-term health problems. If your baby receives breathing support or an IV, it’s typically needed for just two to four days, though some rapid breathing may last for several days. 

Other potential long-term effects include a higher risk of lung infections and wheezing during the first year of life. Newborns who develop MAS may have a greater chance of developing asthma down the road.