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Poop can be pretty gross, but newborn  poop is in a league of its own. Especially a baby’s first poop, or meconium,  which is like a sticky, greenish-black mass that actually forms before the little  one has even had a meal for the first time.

It is unlike any bowel  movement that comes after it. Doctors can use it to get insights into  what that newborn has been through in the uterus, and it can even act as a red flag  for some serious future health issues. Beyond our first few poops,  stool is normally composed of about 75% water and 25% solid matter.

About a third of that solid matter is dead  gut bacteria, another third is indigestible cellulose from food, and the rest is a varying  mixture of fats, proteins, and inorganic substances like minerals  that your body didn’t use. It also contains things like dead cells, bile, and stuff your body just needs to get rid of. But newborn poop is a different  story because fetuses in utero don’t really eat the way we do.

Instead of getting nutrients from food, the  fetus gets nutrients from the placenta, an organ that develops in the  uterus during pregnancy. The nutrients travel from  the placenta to the fetus through the umbilical cord’s blood vessels. And it seems like newborns don’t  have bacteria in their gut, either.

We have some good evidence of this  from a tightly controlled study on the microbiome of meconium published  in Nature Microbiology in 2021. Instead of taking samples of meconium in  the days after birth, this study took swab samples from babies born by cesarean section. They even lifted the babies’ butts out  of the incision to take the sample before pulling the rest of the baby out so  that they could avoid bacteria from the environment or birth process establishing  itself and possibly skewing the results.

When they analyzed those very carefully  taken poop swabs, the researchers found that there were no signs of  an established gut microbiome in the meconium at birth. Once it develops, the gut microbiome is  full of microbes from bacteria to viruses and fungi, the majority of  which are helpful to our bodies. Now, you may be thinking: If there’s no  bacteria in the baby’s gut, and there’s no food in the womb, what the  heck is the poop doing there?!

Well, meconium is made up of a whole host of materials ingested during development. Stuff like skin cells, amniotic  fluid, and various molecules that are products of metabolism,  known as metabolites. There's also lanugo in there, which is a  kind of fine white hair that babies develop, then shed and then subsequently ingest, in utero.

All these things all add up to one  tarry, green-black, sticky poop. And the meconium the baby doesn’t eliminate  at first is a source of nutrients for the microbes that will later  become established in the gut. Now, you would not necessarily always  find this stuff in a baby’s first diaper.

If there are stressors in the womb, like  an issue with getting enough oxygen, the fetus may become stressed and pass  their meconium before they’re born. It then enters the amniotic fluid, and  could make its way into the fetus’ lungs, causing a condition known as  Meconium Aspiration Syndrome, or MAS. Doctors will diagnose MAS in newborns  exhibiting breathing issues born alongside meconium-green-tinted amniotic fluid,  which would otherwise be clear, like water.

As you might imagine, the  lungs are not a great place for poop to end up, even if it’s sterile poop. It can clog the baby’s airways,  irritate and damage tissue, and prevent the lungs from  opening up properly after birth. Babies with MAS might be given  supportive treatments, like oxygen, or in more severe cases even  put onto a ventilator and given specific treatments to help  the lungs open up fully.

But even when babies pass meconium normally,  there’s also a lot that doctors and researchers can learn from it that can  help those babies further down the line. Since it’s composed of all these  elements that the baby has been exposed to in the womb, it can  act kind of like a time capsule. And analysis of meconium can tell  us what kinds of molecules were passing from parent to baby during gestation.

That means it's a good way to spot  things like any drug exposures that may have affected development. For example, in a 2006 study,  researchers found that analysis of certain fatty acid ethyl  esters, also known as FAEEs, in a baby's first bowel movement  could indicate exposure to alcohol. The researchers examined 124 parent/infant pairs.

When asked about alcohol consumption, 93 of the parents said that they had  consumed alcohol during the pregnancy, and the remaining 31 had not. Then, researchers searched for  chemical compounds in the meconium that correlated with reported  levels of alcohol consumption. They identified molecules by breaking them  into little pieces and figuring out what the molecular weights of the  pieces were, a technique called positive chemical ionization gas  chromatography/mass spectrometry.

Their results showed that levels of FAEEs  had a strong correlation with levels of alcohol consumption, although the  researchers could only identify some of the parents who consumed  alcohol based on that measurement. And this wasn't just an interesting  finding for its own sake. It also pointed to this compound as  potentially harmful to fetal brain development, which may help us gain further  insights for treatments in the future.

In fact, doctors are already  able to use FAEE levels as an alert for possible future cognitive issues. And it’s not just alcohol's effects we  can observe through the first poops. Another study has shown that chemicals from cigarette  smoke showed up in meconium.

And the amounts of those chemicals  correlated strongly with the extent of the parent’s cigarette exposure or consumption. And we’re able to get all of that information  from this little poop time capsule thanks to the fact that it formed  before the baby was even born - let alone had their first meal. So, even though it looks super gross,  meconium can provide a whole host of scientific information on what the  baby has been exposed to in the womb, and even help us to support  that baby’s future needs.

Which is a pretty neat trick  for just a full gross diaper. Thanks for watching this episode of SciShow! And thank you so much to all of our patrons  for making it possible for us to share free science education videos like this one.

I know when you clicked that  button, when you became a patron, you were thinking, “I hope  I get a baby poop episode.” If you’d like to learn more about becoming  a patron and joining our community, you can check out patreon.com/scishow. [♪OUTRO].