What Happens When Babies Poop in the Womb

It's no secret babies poop a lot once they are born. But did you know they 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, a registered nurse who has experience in labor and delivery, postpartum, neonatal, and the NICU.

Learn more about why babies might poop in the womb, and what happens if they accidentally inhale it.

What Is Your Baby’s First Poop?

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, MD, 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. It may take up to 48 hours, but anything longer than that should be evaluated.

Once meconium passes, a baby’s poop is expected to change color, smell, and consistency. But an appearance of a baby’s poop depends on whether they are breastfed or formula-fed. A baby who nurses will usually have softer stool that is more yellow. A baby who formula feeds will usually have darker and more odorous poop.  

When Babies Poop in the Womb

Sometimes, meconium can come out when a fetus is still inside the womb, where it mixes with amniotic fluid (the liquid that surrounds the fetus in utero). In fact, according to a 2020 study, anywhere from 12 to 20% of fetus's poop in utero. When the pregnancy is past its due date, the number increases to around 40%. Pooping in the womb rarely happens with premature babies.

Some factors that increase the risk of passing meconium in utero include:

• Fetal distress from inadequate blood or oxygen level
• Issues with the placenta or umbilical cord
• 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
• Amniotic fluid issues
• Preeclampsia 

Risks of Passing Meconium in the Womb

Meconium is actually quite clean; it consists of mostly water and doesn't cause infection of the uterus, says Faulkner. But while most fetuses who poop in the womb don't experience negative side effects, anywhere from 4% to 10% 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.

Symptoms of Meconium Aspiration Syndrome (MAS)

Health care providers 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 (Pregnant people might also notice this when their water breaks—and if so, they should tell their health care provider 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 MAS

Poop in the womb doesn't always call for treatment, especially if the baby appears happy and healthy after birth. However, if a newborn has MAS, health care providers 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," says Faulkner.

Extreme cases of MAS might require additional intervention, adds 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 research shows MAS increases the risk of asthma later in life, most babies don't have any long-lasting side effects.

Do Babies Fart in the Womb?

While developing fetuses can poop in the womb, passing gas is another matter entirely. In order to pass gas, or "fart," individuals need to ingest air. Since fetuses do not take their first breath until after birth, this means farting in the womb is not just improbable, it is impossible.

Do Babies Pee in the Womb?

Unlike pooping, a fetus is expected to urinate in the womb. A fetus absorbs nutrients through the placenta when they're inside the womb. The waste usually exits their bodies as urine. Urine typically begins between week 13 and week 16 of pregnancy when a fetus’s kidneys are formed. And the fetus’s urine will start to make up the majority of amniotic fluid around 20 weeks.