Gut bacteria found in children delivered by cesarean section largely reflected the bacterial surroundings of the hospital in which the baby was born, British investigators report.
That wasn't the case among children born vaginally. Their gut mostly mimicked the bacterial environment of their mother.
"This is the largest genomic investigation of newborn babies' microbiomes to date," said senior study author Trevor Lawley, from the Wellcome Trust Sanger Institute, a nonprofit British genetics research organization. "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."
But the researchers stressed that by age 1, all children, regardless of delivery method, end up having pretty similar gut microbiomes.
It also remains unclear whether the differences seen at birth actually have any long-term health implications. And the finding, experts said, should not deter patients from undergoing a C-section when warranted.
"The first weeks of life are a critical window of development of the baby's immune system, but we know very little about it," said principal study author Dr. Peter Brocklehurst, a professor of women's health from the University of Birmingham.
"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," he added in a Wellcome news release. "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."
Meanwhile, senior author Nigel Field, from University College London, emphasized the study shows "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.
"After they have been weaned, the microbiome differences between babies born via caesarean and delivered vaginally have mainly evened out," Field said in the release.
The study was published Sept. 18 in the journal Nature.
Despite the findings, "in many cases, a cesarean is a lifesaving procedure, and can be the right choice for a woman and her baby," said Dr. Alison Wright, vice president of the Royal College of Obstetricians and Gynaecologists in London.