Right now, you’re carrying a microscopic hand-me-down from your mom that you’ve had since the moment you were born: The microbiome. We get a mouthful of this diverse teeny tiny community of bacteria and other microorganisms as we slip and slide out of our moms, and it’s further shaped and pruned by our environment, diet, lifestyle, and even genetics.
Studies so far have suggested that how we are born — whether via cesarean section or vaginal birth — plays an influential role in shaping our microbiomes. Babies born the surgical route appear to miss out on that healthy dose of vaginal (and poop) bacteria like Bacteroides that colonize the gut in early life and play a role in keeping us hale and hardy.
But according to a study published Thursday in the journal Cell Host & Microbe, our infant microbiomes appear to have ways to fill in the gap. A group of Scottish and Dutch researchers found that microbiomes of cesarean-born babies during the first month of life are able to compensate for the microbial deficit through their mother’s breastmilk.
“We have known for some time that breastfeeding is beneficial for the baby gut microbiota because it has indigestible carbohydrates that, like fiber, the baby cannot digest, but is food for microbes,” Maria Gloria Dominguez-Bello, a professor of microbiology at Rutgers University, who was not involved in the study, told Inverse in an email.
“But this paper beautifully shows the mother-child transmission of microbiota in different body sites, and how breastfeeding can restore, at least partially, the microbiome of babies born… by [cesarean] section.”
Breastfeeding, the great microbial equalizer
The task involved tracking how the baby’s microbiome develops and changes during the first month of life. To do that, the researchers recruited 120 Dutch soon-to-be mothers. The moment their babies were born, the infants were swabbed for various microbiome samples at different time points — the skin, nose, saliva, and poop at two hours old, a day old, one week old, two weeks old, and one month old.
These samples were analyzed against swabs collected from the moms from the same microbial niches but including two others — breastmilk and vaginal microbiomes. The bacterial species contained in the mother’s samples were analyzed against their babies, taking into account other factors that could influence microbiome transfer like delivery mode, antibiotic use after delivery, breastfeeding, and even the presence of older siblings.
During a baby’s first month, the microbiome’s diversity appeared to be a gradual build-up, particularly when it comes to gastrointestinal microbes compared to those on the skin or lining the respiratory tract. But the diversity seems to rapidly taper off during the first week of life before picking up again, a trend that’s been noticed by other studies in the past.
Unsurprisingly, the mom’s fecal microbiome played a role in seeding the infant gut microbiome more so in babies born vaginally (in line with previous research). But the team saw that cesarean-born babies whose mothers had a trial of labor before delivery still managed to get some exposure to the vaginal microbiome compared to babies whose mothers didn’t.
“We saw that many niches of the mother are important for the transmission of microbes, and if some of these pathways are blocked for one reason or another — in this case, we saw that happening with the cesarean section — then these microbes can still reach the infant through other paths,” Wouter de Steenhuijsen Piters, the study’s lead author and a physician at the University Medical Center Utrecht in the Netherlands, said in a press release.
And one of those compensatory pathways was breastmilk. This microbiome, in particular, seemed to be the niche most important for seeding the infant gastrointestinal microbiome in cesarean-born babies compared to their vaginally born counterparts. One reason for this, the researchers speculate, is that the lack of exposure to the mother’s fecal microbiome gives leeway to healthy microbes in breastmilk to colonize these otherwise sparsely inhabited niches, so to speak.
What’s next for the research
For Kjersti Aagaard, a maternal-fetal medicine specialist and professor of obstetrics and gynecology at Baylor College of Medicine, who was not involved in the study, these results aren’t surprising. In 2017, she and colleagues published a similar study in the journal Nature Medicine that looked at the development of multiple microbial niches in babies over time and arrived at similar findings. Another 2020 study published in the journal BMC Pediatrics also found that breastfeeding appeared to restore the infant gut microbiome
“The old way of thinking was [that] vaginal microbes populated the [infant] at the time of birth, and in the absence of them, nothing went right,” Aagaard tells Inverse. “But that’s not actually true. Plenty goes right, and especially in babies that are exclusively breastfed, that seems to play a very nice role in establishing their microbiome.”
She hopes these findings will open up a dialogue of destigmatizing cesarean section — soon-to-be moms may feel electing for a surgical delivery may put their baby’s health at a microbial disadvantage — but also a consideration that we shouldn’t be too hung up on whether our microbiomes are getting any particular bacteria since many of them share similar functions.
“We can’t just think about [whether] we have a smidge more of one bacteria and a smidge few of another, we really have to look at overlapping and redundant functional pathways of these microbes,” says Aagaard. “We need to think about what [these bacteria] are doing and capable of doing rather than what’s there and what’s not.”
It’s also important to note the study looked at mothers and babies in the Netherlands, which may not necessarily be representative of all mothers and babies in the world, says Michael Bailey, associate professor of pediatrics at The Ohio State University Medical School.
“It’s a good sample size, but it’s still a limited sample, and we don’t know how it’s going to translate to other populations,” he explains to Inverse.
The researchers also found that for all the infants studied, about 60 percent of their microbiomes were derived from their moms; 40 percent were due to other factors, some known and unknown.
“There may be additional factors at play that we really don’t have any hints about at this time,” says Bailey.
But that’s an upcoming item to tackle on the research agenda, along with a better understanding of how infant microbiome coalesces and contributes to long-term health.
“Next, we want to explore whether this early life process, influenced by mom, is affecting not only short-term infection risk in the first year of life but also longer-term health in terms of things like allergies and asthma,” Debby Bogaert, the study’s first author and a physician at the University of Edinburgh, said in a press release. “In the future, we might be able to utilize this knowledge to help prevent, diagnose, or treat health problems.”
