Baby's gut bacteria affected by delivery method

UK researchers have confirmed that babies born vaginally have different gut bacteria than those delivered by caesarean. Whereas vaginally born babies got most of their gut bacteria from their mother, babies born via caesarean had more bacteria associated with hospital environments in their guts. Their study has been published in the journal Nature.

The gut microbiome is a complex ecosystem of millions of microbes and is thought to be important for the development of the immune system. Lack of exposure to the right microbes in early childhood has been implicated in autoimmune diseases such as asthma, allergies and diabetes. However, it is not fully understood how important the initial gut microbiome is to the baby’s immune system development and health, how a baby’s microbiome develops or what happens to it with different modes of birth.

To understand more about the development of the microbiome, researchers studied 1679 samples of gut bacteria from nearly 600 healthy babies and 175 mothers. Faecal samples were taken from babies aged four, seven or 21 days old, who had been born in UK hospitals by vaginal delivery or caesarean. Some babies were also followed up later, up to one year of age.

Using DNA sequencing and genomics analysis, the researchers could see which bacteria were present and found there was a significant difference between the two delivery methods. They discovered that vaginally delivered babies had many more health-associated (commensal) bacteria from their mothers than babies who were born by caesarean.

“This is the largest genomic investigation of newborn babies’ microbiomes to date,” said Dr Trevor Lawley, a senior author on the paper from the Wellcome Sanger Institute. “We discovered that the mode of delivery had a great impact on the gut bacteria of newborn babies, with transmission of bacteria from mother to baby occurring during vaginal birth.”

Previous limited studies had suggested that vaginal bacteria were swallowed by the baby on its way down the birth canal. However, the large-scale study found babies had very few of their mother’s vaginal bacteria in their guts, with no difference between babies born vaginally or by caesarean.

Rather, the study discovered it was the mother’s gut bacteria that made up much of the microbiome in the vaginally delivered babies, with babies born via caesarean having fewer of these bacteria. It therefore found no evidence to support controversial ‘vaginal swabbing’ practices, which could transfer dangerous bacteria to the baby.

In place of some of the mother’s bacteria, the babies born via caesarean had more bacteria that are typically acquired in hospitals and were more likely to have antimicrobial resistance. The researchers isolated, grew and sequenced the genomes of more than 800 of these potentially pathogenic bacteria, confirming that they were the same as strains causing bloodstream infections in UK hospitals. Although these bacteria don’t usually cause disease while in the gut, they can cause infections if they get into the wrong place or if the immune system fails.

All women who have a caesarean are now offered antibiotics before the delivery to help prevent the mother developing postoperative infections, meaning that the baby also receives a dose of antibiotics via the placenta. This could also cause some of the microbiome differences seen between the two birth methods.

The exact role of the baby’s gut bacteria remains unclear, and it isn’t known if these differences at birth will have any effect on later health. The researchers also found the differences in gut bacteria between vaginally born and caesarean delivered babies largely evened after one year, but large follow-up studies are needed to determine if the early differences influence health outcomes.

“Our study showed that as the babies grow and take in bacteria when they feed and from everything around them, their gut microbiomes become more similar to each other,” said Dr Nigel Field, a senior author on the paper from University College London. “After they have been weaned, the microbiome differences between babies born via caesarean and delivered vaginally have mainly evened out. We don’t yet know whether the initial differences we found will have any health implications.”

“We urgently need to follow up this study, looking at these babies as they grow to see if early differences in the microbiome lead to any health issues,” added Professor Peter Brocklehurst, Principal Investigator of the Baby Biome Study from the University of Birmingham. “Further studies will help us understand the role of gut bacteria in early life and could help us develop therapeutics to create a healthy microbiome.”

Image credit: ©stock.adobe.com/au/Cari

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