What is already known
Scientists have long thought that the exposure of newborns to their mothers’ vaginal microbiota during delivery influences the development of the babies’ community of gut microbes. As a result, vaginal seeding — the practice of soaking cotton gauze with vaginal fluid to transfer the bacteria to the mouth, nose or skin of a newborn infant — has risen in popularity. But the effect of the maternal vaginal microbiota on that of the infant gut remains unknown.
What this research adds
Researchers analyzed the effect of the maternal vaginal microbiota on the development of the infant gut microbiota at 10 days and three months after birth. Regardless of birth mode, a mother’s vaginal microbes did not predict the composition of babies’ gut microbiota. However, the researchers did find differences between newborns’ gut microbiota in early life, likely due to exposure to antibiotics around the time of birth.
Conclusions
The findings show that a mother’s vaginal microbiota does not affect infant gut microbiota composition and development.
Scientists have long thought that the exposure of newborns to their mothers’ vaginal microbiota during delivery influences the development of the babies’ community of gut microbes. But one of the largest mother-infant studies to date appears to upend this idea.
The study found that a mother’s vaginal microbiota is not a key determinant of her infant’s gut microbiota composition and development during the first months of life. The findings, published in Frontiers in Cellular and Infection Microbiology, suggest that practices to change the infant gut microbiota should focus on factors other than maternal vaginal microbes.
Previous research suggested that babies delivered via Cesarean section may lack the natural immunity of babies born vaginally, likely because C-section babies aren’t exposed to their mother’s vaginal bacteria at birth. As a result, vaginal seeding — the practice of soaking cotton gauze with vaginal fluid to transfer the bacteria to the mouth, nose or skin of a newborn infant — has risen in popularity.
Several studies found that exposing C-section babies to their mother’s vaginal fluids appeared to help the infants to develop a microbiota similar to that of babies born vaginally. But the effect of the maternal vaginal microbiota on that of the infant gut remains unknown.
Janet Hill at the University of Saskatchewan, Deborah Money at the University of British Columbia and their colleagues analyzed the effect of the maternal vaginal microbiota on the development of their infants’ gut microbiota at 10 days and three months after birth.
Early diversity
The researchers recruited 621 Canadian pregnant women who planned to deliver either vaginally or through a C-section. The team collected vaginal swabs from the mothers before delivery and stool samples from newborns within 72 hours of delivery, at 10 days and three months of life.
Most 10-day-old infants had a gut microbiota dominated by bacteria such as Escherichia coli and various members of the genera Bifidobacterium, Enterococcus, Klebsiella, Bacteroides and Streptococcus. Newborns’ stool samples could be grouped into 25 clusters: 23 clusters were characterized by a single dominant species, one was characterized by a mixture of E. coli, Bifidobacterium breve and Parabacteroides distasonis, and a third cluster was composed of multiple bacterial species.
At 3 months, the diversity of the infant gut microbiota as well as the abundances of E. coli and Bifidobacterium bacteria increased. The number of bacterial groups decreased to 14, with 12 clusters characterized by a single species.
Confounding factors
The team found that, at 10 days after delivery, the infant gut microbiotas showed significant differences in composition by delivery mode. Bacteria such as Klebsiella, Enterococcus and Streptococcus parasanguinis were overrepresented in stool microbiotas of C-section babies, whereas E. coli as well as Parabacteroides, Bacteroides and Bifidobacterium species were more common in vaginally-delivered infants.
However, these differences were reduced at three months of life and could not be explained by the composition of the maternal vaginal microbiota. The differences between newborns’ gut microbiota in early life were most likely due to exposure to antibiotics around the time of birth, the team found.
The researchers did not collect maternal stool samples, so they couldn’t rule out the influence of the mother’s gut microbes on her infant’s microbiota. However, the findings suggest that exposure to the maternal vaginal microbiota at the time of birth does not affect infant gut microbiota composition and development in early life.
