After nine months of growing in someone else’s body, the second a baby is born, it begins to grow inside its own body: colonies of tiny bacterial cells ready to begin populating the gut microbiome of ‘a baby. This microbial starter pack is a kind of parting gift from the mother’s body, acquired by a baby during the journey from the womb through the birth canal. As a baby grows, its internal ecosystem becomes more complex, until it has finally developed the robust bacterial diversity that allows the intestine and other microbial refuges to regulate and protect immunity and so many other elements of health.
This method of microbial transfer is a great evolutionary game plan. But in the modern world, there is a problem: not all babies take the same path. Do infants born via C-section receive the same bacterial benefit as those born vaginally?
The answer is no, and the question of how to address this deficit is at the heart of an emerging field of research. It is also an issue of increasing importance as the rate of caesarean deliveries continues to rise in the United States By missing the vaginal canal, babies born by caesarean section are less exposed to germs at birth, but a document published on March 8 in the magazine Cell host and microbe suggests that there may be ways to compensate for this loss in the first few weeks of life.
There’s no doubt that vaginal births transmit more beneficial bacteria than C-sections, says Dr. Wouter de Steenhuijsen Piters, physician and data scientist at University Medical Center Utrecht in the Netherlands and lead author of the study. “When you compare emergency caesareans – when a woman has already given birth and the child has already partially passed through the birth canal – and elective caesareans, children [in the first category] more like vaginal newborns,” he explains. Previous studies have looked at methods of compensating for missed microbial exposure, the most notable of which involves a practice called vaginal seeding, in which a mother’s vaginal and sometimes fecal excretions are transferred into the mouth or skin of a infant caesarean shortly after birth. These tactics have proved usefull for the infant microbiome, but some experts have expressed concern about the associated risks, such as the unwanted transfer of harmful bacteria or viruses, including STIs. Ultimately, says Dr Debby Bogaert, a pediatric researcher at the University of Edinburgh and lead author of the study, this practice is often simply not enough to completely fill the void.
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The potential consequences of insufficient exposure to bacteria at birth are fairly well understood. “For a long time, caesarean birth itself has been associated with certain outcomes, for example obesity, type 1 diabetes and allergies,” says de Steenhuijsen Piters. And the link is more than associative, he adds. Specific microbial differences in cesarean babies have been shown to cause directly some of these health conditions.
But despite all the differences, says Bogaert, the mere fact that babies born by caesarean live and grow shows that “every child is colonized. And the question was, where did these bacteria ultimately come from? And do they come from the mother, from other sources or from the environment?
In their new study, Bogaert and de Steenhuijsen Piters found that when babies born by C-section are breastfed, the microbes they receive from breast milk appear to make up for the lack of microbes from other initial sources. “It was just unheard of,” says Bogaert. “We have only been able to do these studies for a few years. We didn’t know that and we hadn’t thought about it.
Bogaert and Steenhuijsen Piters’ research followed 120 Dutch mothers and babies, collecting samples of the infants’ skin, nose, saliva and gut microbiome at two hours, one day, one week, two weeks and one month after birth. birth. At each stage, they compared the unique microbiota they found to that of six different microbial hotspots on the infants’ mothers: their skin, breast milk, nose, throat, vagina and feces. “We said, ‘Let’s try to put it all in a holistic context – the whole mother and the whole baby,'” says Bogaert.
In all infants, regardless of delivery method, an average of 58.5% of their microbial landscape could be traced directly back to their mother – a number they say reiterates the importance of things like skin-to-skin contact (including kissing and cuddling) in an infant’s first weeks. Even more interesting was their finding that how babies were born seemed to influence where most of their bacterial colonies originated on their mothers. In analyzes of babies’ feces two weeks after birth, the percentage of the infant microbiome that could be attributed to maternal fecal contributions was twice as high in babies born vaginally as in babies born by caesarean section. However, these same C-section babies received almost a third of their microbiome from breastfeeding, while the bacterial breakdown of vaginally born infants comprised only 11.2% that was attributable to breast milk. While some specific bacteria may still be missing, there is also a remarkable amount of overlap between different areas of the body, which means breastfeeding does a lot of compensatory work to develop a baby’s systems. The authors also found that babies born by C-section who drink exclusively formula milk lack the rich microbiome that other C-section babies accumulate from breast milk.
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“Everything the baby receives from the mother seems important,” says Bogaert. Breastfeeding even transmits germs not only through milk, but also through skin contact. Bogaert says she would advise new mothers to hold and kiss their baby a lot and “really try to invest in breast milk, even if it doesn’t work the first few days. If you can even try to breastfeed a little, all those germs could mean a lot to your baby. She says she would also like to see fellow pediatricians be more judicious when administering antibiotics to newborns, as the drugs can disrupt their microbiota.
Bogaert and her colleagues acknowledge that when it comes to newborns, there is often a fine line between encouraging empirical best practices and shaming new mothers for their choices – and what is simply realistic, given that the breastfeeding takes a long time and requires workplace support, which is often insufficient. “I really, really believe that knowledge is power,” she says. “I have two teenagers. When they were born, we didn’t have this knowledge. And I wish it had, because it might have helped me and other moms and dads make some decisions.
Maria Gloria Dominguez-Bello, a Rutgers professor who also studies the microbiota in early life and was not involved in the study, hopes research like this will help bring about societal change on a larger scale than it deems necessary to reduce the number of elective caesarean sections. She likens childbirth to running a marathon, but with one key difference: runners “have so much support. They have a rescue team providing them with water and massaging their legs. By contrast, in many communities Dominguez-Bello has worked with, “mothers give birth alone,” she says. “Every woman has the right to have a team that supports her during childbirth.” When she sees skilled teams like this in action, she says, “You hear women say, ‘I had a fabulous experience giving birth.’ Society must provide a structure that helps mothers and babies.
Experts agree that more research is needed to improve the birth experience and critical days of infancy, regardless of how a baby is born. For Bogaert and de Steenhuijsen Piters, that means analyzing the rest of the data they collected while tracking their cohort through infancy and into childhood, to better understand the impacts of specific microbial differences. They also hope to break down more detailed information about where the remaining 40% of an infant’s microbiome comes from, looking at factors like fathers, siblings, hospital environments, pets, and more.
But for now, one takeaway from their research that all new parents and expectant parents can put to good use, they say, is to really go out there and cuddle your newborn.
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