Newborns delivered by C-section tend to have more gut microbes associated with hospitals than their vaginally delivered peers, according to a study published today (September 18) in Nature—but the health effects, if any, of that difference are unclear.

Previous studies have linked C-sections with an increased risk of conditions such as asthma and diabetes, leading some researchers to suspect that babies born in this way may have different mixes of gut bacteria because of their lack of exposure to the birth canal. But studies of whether babies born by C-section do have microbiomes that are distinct from vaginally delivered infants have yielded conflicting results.

“Caesarean sections are a life-saving and medically necessary intervention,” says Lisa Stinson, a molecular microbiologist and reproductive biologist of the University of Western Australia who was not involved in the new study, in an interview with Science News....

The new analysis, part of a longer-term effort called the Baby Biome Study, is the largest so far to address that question. Researchers collected the poop of 314 newborn babies born vaginally and 282 born by C-section in the UK, and tested which bacteria were present. While the guts of the vaginally born babies had been colonized by the commensal bacteria typically found in healthy people, those delivered by C-section had microbiomes dominated by species commonly found in hospitals, such as those in the genera Enterococcus and Klebsiella.

“The level of colonization by health-care pathogens is shocking in these children. When I first saw the data, I couldn’t believe it,” coauthor Trevor Lawley, a microbiologist at the Wellcome Sanger Institute, tells Nature

The researchers resampled some of the same babies’ fecal matter later, when the infants were about 9 months old, and found the gut microbes of the two groups had become more similar. The C-section babies remained lower in commensal Bacteroides species, however. 

“The first weeks of life are a critical window of development of the baby’s immune system, but we know very little about it,” coauthor Peter Brocklehurst of Birmingham University tells Reuters. “We need to follow up . . . these babies as they grow to see if early differences in the microbiome lead to any health issues.”

See “How Do Infant Immune Systems Learn to Tolerate Gut Bacteria?

Shawna Williams is an associate editor at The Scientist. Email her at swilliams@the-scientist.com or follow her on Twitter @coloradan.

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a baby just born by c-section

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