The composition of gut microbes in babies born via Cesarean section tends to differ from those in babies born vaginally, prompting speculation that this may have long-term health consequences. To enrich for beneficial bugs in babies’ bellies after C-section, researchers have performed mom-to-infant microbial transplants, described today (October 1) in Cell. In a clinical trial in which seven Cesarean-delivered babies were fed tiny amounts of their mothers’ fecal material, it was found that the babies’ guts became colonized with the sorts of bacteria normally present in infants delivered vaginally. While the procedure produced no ill effects in the infants, there are no data on whether it has any benefits to the baby, and experts warn it may be dangerous for mothers to attempt such a treatment themselves.

“This is a very well-balanced, important, and clinically relevant contribution to the field, with really nice, clear-cut...

As a baby leaves the womb and passes through the birth canal it is bathed in its mother’s microbes—an experience that Cesarean-born infants do not share. As a result, there are differences in the bacteria that colonize the guts of newborns depending on their delivery method.

Epidemiological evidence indicates there may also be later life consequences to missing out on this bacterial baptism, as some call it. A recent study showed that Cesarean-born kids have a higher likelihood of developing immune disorders such as inflammatory bowel disease, rheumatoid arthritis, and celiac disease. The growing prevalence of Cesarean deliveries makes these potential repercussions an increasing concern.

Numerous trials are therefore underway to test the safety and long-term benefits of swabbing Cesarean-born infants with microbes from their mothers’ vaginas. But, there aren’t a lot of published data to suggest that the gut microbiomes of these swabbed infants match those of vaginally born babies, says microbiologist and immunologist Willem de Vos of the University of Helsinki and Wageningen University who led the research. Furthermore, he adds, “the bacteria that you find in the baby [gut] are not found in the vagina, so it’s not so likely it’s the source,” he says. “It’s more likely that there is a fecal-oral transfer” at the time of birth, he says, because vaginal delivery is “a messy business.”

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Indeed, anecdotal accounts suggest most women delivering babies vaginally do defecate during labor. “Feces is always part of the delivery process,” agrees obstetrician Bo Jacobsson of the University of Gothenburg who was not part of the research team. He says he therefore thinks that “from a scientific point of view, [the researchers] have done the right thing,” even if on first impression the procedure seems “nasty.”

A mother’s fecal microbes, unlike those from the vagina, are “geared to actually establish and colonize in the [baby’s] gut, because they come from the gut,” explains Licht. So what de Vos and colleagues have done, she says, “makes sense.”

The team recruited 17 mothers who were due to undergo elective C-sections and collected stool and blood samples from them approximately three weeks prior to delivery. This gave the team time to prepare the samples and to screen them for infectious pathogens, including HIV, hepatitis, Clostridium difficile, Helicobacter pylori, norovirus, drug-resistant bacteria, group B streptococcus, and a long list of others. On the basis of these screens, only seven of the mothers were selected to continue with the procedure.

Each newly delivered baby was given a dose of the live fecal bacteria (a few million cells) in their first milk feed (via a bottle) and their health was monitored for two days in the maternity ward with follow up visits at four weeks and three months. None of the babies experienced adverse health effects.

Stool samples from the babies were collected after two days, then each week for four weeks and then again at 12 weeks. Analysis of these samples as well as of control samples collected from 29 vaginally born babies and 18 untreated Cesarean-delivered babies showed that the while the gut microbiota of the treated and vaginally born babies differed in the early days, after a week they were significantly more similar to each other, and both were distinct from the microbiotas of untreated Cesarean babies. Using previously published data on the microbiota of Cesarean infants who received vaginal swabs, the team showed that these were also distinct from those of the vaginally born or feces-fed infants.

The main differences observed between untreated Cesarean babies and those delivered vaginally or fed feces were that the control infants had a lower abundance of commensal Bacteroides and Bifidobacteria species, but a higher abundance of more pathogenic taxa, in line with previous findings.

While the study provided a proof-of-concept for the procedure, larger and longer-term studies would be necessary to confirm safety and to determine whether there are any health benefits, says Jacobsson. Because of these unknowns, both he and de Vos warn mothers undergoing Cesareans not to try this themselves.

“[There’s] a big risk that people will read about this and make the mistake of doing it themselves,” Jacobsson says, “But, you can put your baby into danger if you start to do a home-style version.”

K. Korpela et al., “Maternal fecal microbiota transplantation in cesarean-born infants rapidly restores normal gut microbial development: a proof-of-concept study,” Cell, doi:10.1016/j.cell.2020.08.047, 2020.

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