Anywhere from 12 to 20 percent of babies poop in the womb. While it’s not usually cause for concern, infants can sometimes inhale poop-stained amniotic fluid, leading to meconium aspiration syndrome. Here’s what parents need to know.

By Nicole Harris
Updated October 16, 2020
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Babies absorb nutrients through the placenta when they’re inside the womb. The waste usually exits their bodies as urine, but babies will occasionally poop before being born. This is only cause for concern if they inhale the fecal matter, which can lead to pneumonia, lung problems, or respiratory distress, says Jeanne Faulkner, R.N. Keep reading to learn more about why babies might poop in the womb, and what happens if they accidentally inhale it.

Why Do Babies Poop in the Womb?

Known as meconium, a baby’s early poop is a black or dark green, thick, sticky substance almost like tar. It’s is made up of intestinal cells, lanugo (the downy hair some babies are born with), mucus, amniotic fluid, bile, and water, says Bradley Howard Kessler, M.D., director of pediatric gastroenterology at Good Samaritan Hospital Medical Center, in West Islip, New York. 

Most of the time, babies expel this meconium on their first day of life. But according to Faulkner, it can sometimes come out when they’re still inside the womb, where it mixes with amniotic fluid (the liquid that surrounds the baby in utero). Some factors that increase the risk of passing meconium in utero include:

  • Fetal distress from inadequate blood or oxygen levels. Issues with the placenta or umbilical cord can cause this to happen.
  • Going past the due date
  • A long and hard delivery
  • High blood pressure, diabetes, or other maternal health issues
  • Smoking during pregnancy
  • Poor intrauterine growth

How often do babies poop in the womb? Meconium is present in about 12 to 20 percent of deliveries, according to a 2020 study. When the baby is past their due date, the number increases to around 40 percent. Pooping in the womb rarely happens with premature babies.

What Happens After Babies Poop In Utero?

Meconium is actually quite clean; it consists of mostly water and doesn't cause infection of the uterus, says Faulkner. But while most babies who poop in the womb don’t experience negative side effects, anywhere from 4 to 10 percent develop meconium aspiration syndrome (MAS).

MAS occurs when poop is inhaled into the lungs through forceful gasps before, during, or after delivery. It can cause airway obstruction, lung inflammation, and problems with oxygen exchange. Severe or untreated MAS also increases the risk for pneumonia, collapsed lung, and other respiratory conditions in newborns.

Doctors are trained to recognize the symptoms of meconium aspiration syndrome, and they might confirm the diagnosis with a chest X-ray after delivery. Symptoms of MAS include:

  • Green meconium-stained amniotic fluid (Women might also notice this when their water breaks—and if so, they should tell their doctor right away.)
  • Meconium stains on the baby
  • Breathing issues
  • Bluish skin color because of low blood oxygen levels
  • Limp body
  • Low Apgar scores
  • Slow heart rate (possibly detected by a fetal monitor before birth)

Treating Meconium Aspiration Syndrome

Poop in the womb doesn’t always call for treatment, especially if the baby appears happy and healthy. However, if a newborn has meconium aspiration syndrome, doctors will immediately suction their mouth, nose, and airways to remove the contaminated fluid. “Babies that are born not breathing, floppy, or with cardiac problems get suctioned and resuscitated until they perk up,” adds Faulkner. 

Babies with extreme cases of MAS might require additional intervention, says Faulkner. Depending on the specific case, this can include oxygen supplementation, breathing assistance with a ventilator, antibiotics, methods to maintain normal body temperature, IV nutrition, administration of surfactant, and nitric oxide inhalation. Babies with severe MAS might stay in the NICU, where they’re “watched and treated carefully,” says Faukner. 

Most babies with MAS get better within days or weeks. Parents might notice rapid breathing for a bit, but permanent lung damage is extremely rare. And although some experts believe MAS increases the risk of asthma later in life, most babies don't have any long-lasting side effects.

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