Vaginal Microbiome Does Not Affect Infant Gut Microbiome

Contrary to popular belief, an infant's gut microbiome is not primarily shaped by the mother's vaginal microbiome, a new study indicates. The findings suggest that practices such as vaginal seeding are ineffective.

A longitudinal, prospective cohort study of more than 600 pregnant Canadian women and their newborns showed significant differences in an infant's stool composition by delivery mode at 10 days post partum, but the differences could not be explained by the mother's vaginal microbiome, and they effectively disappeared by 3 months.

Scott Dos Santos

The findings were surprising, Scott Dos Santos, a PhD candidate at the University of Saskatchewan in Saskatoon, Canada, told Medscape Medical News. "The bacteria living in the maternal vagina are the first microbes that vaginally delivered infants are exposed to...so it sounds intuitive that different kinds of vaginal microbiomes could end up influencing the development of a baby's gut microbiome in different ways. But the maternal vaginal microbiome didn't seem to have any role in predicting what the infant stool microbiome looked like."

Therefore, women should not be concerned about cesarean delivery having an adverse effect on their baby's gut microbiome, said Dos Santos. Moreover, "vaginal seeding is not safe or advised. Professional bodies, including the Society of Obstetricians and Gynecologists of Canada and the American College of Obstetricians and Gynecologists, strongly advise against this practice."

The study was published online March 30 in Frontiers in Cellular and Infection Microbiology.

Independent Communities

The investigators analyzed vaginal and stool microbiome profiles from 442 mother–infant dyads. The mothers were healthy, low-risk women who delivered at term. They were recruited into the Maternal Microbiome LEGACY Project from three hospitals in British Columbia.

The mean age of the mothers at delivery was 34.6 years, which is typical of the study hospitals' delivery populations. Participants identified themselves as White (54.7%), Asian (21.2%), South Asian (8.3%), and of other ethnicities.

A nurse, midwife, or clinician collected maternal vaginal swabs of the posterior fornix and lateral vaginal wall at first presentation to the labor and delivery area. Neonatal meconium, which was defined as the first stool specimen collected within 72 hours of birth, and two infant stool samples were collected at follow-up visits at 10 days and 3 months post partum.

A principal component analysis of infant stool microbiomes showed no significant clustering of microbiome profiles at 10 days or 3 months by maternal community state types (that is, microbial species).

Correspondence analyses also showed no co-clustering of maternal and infant clusters at either time. In addition, there were no differences in the distribution of maternal vaginal microbiome clusters among infant stool microbiome clusters, regardless of delivery mode.

Vaginal microbiome clusters were distributed across infant stool clusters in proportion to their frequency in the overall maternal population, indicating that the two communities were independent of each other.

Intrapartum antibiotic administration was identified as a confounder of infant stool microbiome differences and was associated with lower abundances of Escherichia coli, Bacteroides vulgatus, Bifidobacterium longum, and Parabacteroides distasonis.

"Our findings demonstrate that maternal vaginal microbiome composition at delivery does not affect infant stool microbiome composition and development, suggesting that practices to amend infant stool microbiome composition focus on factors other than maternal vaginal microbes," the authors conclude.

More Evidence Needed

Commenting on the study for Medscape, Emily H. Adhikari, MD, assistant professor of obstetrics and gynecology at UT Southwestern Medical Center in Dallas, Texas, and medical director of perinatal infectious diseases for the Parkland Health and Hospital System, said, "These findings contribute significantly more data to an understudied area of research into factors that affect the infant gut microbiome from the earliest hours of life. Prior studies have been small and often conflicting, and the authors reference recent larger studies, which corroborate their findings."

Dr Emily Adhikari

The data regarding whether delivery mode or antibiotic-associated differences in infant microbiomes persist remain controversial, said Adhikari. "More evidence is needed involving a more ethnically diverse sampling of patients." In addition, prospectively evaluating vaginal seeding in a rigorously designed clinical trial setting is "imperative to understand any potential benefit and certainly to understand the potential harms of the practice. To date, this does not exist."

The study was funded by a Canadian Institutes of Health Research grant. Dos Santos and Adhikari have disclosed no relevant financial relationships.

Front Cell Infect Microbiol. Published online March 30, 2023. Full text

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