Does Rubbing Vaginal Fluids on C-Section Babies Improve Their Microbiomes?

Southern Medical University (SMU) scientists led a triple-blind experiment testing the effects of “vaginal seeding” on newborn babies’ microbiomes after a cesarean section (C-section) delivery. The research is published in Cell Host & Microbe.

Birth method and microbiome structure

Emerging research suggests that birth method may impact a newborn infant’s microbiome. Some studies have questioned whether a C-section birth might lead babies to “miss out” on essential microbes derived from their mother’s birth canal. A definitive answer to this question doesn’t yet exist – it’s possible that babies born by C-section obtain important microbes from other sources as a compensatory mechanism. Scientists do know that early microbiome structures are linked to certain health outcomes, such as respiratory infection susceptibility.

The emerging data surrounding birth mode and microbiome composition has led to a rise in practices such as vaginal seeding – also known as vaginal microbe transfer (VMT). Research conducted in small sample sizes has observed some positive effects of this practice, and a mouse model study demonstrated that inoculating C-section-delivered newborns with human-derived vaginal microbes impacted their growth, immunity and brain development. However, robust clinical evidence supporting the safety and effectiveness of vaginal seeding is lacking. 

“When we talk about effectiveness, we not only mean whether this intervention might affect the infants’ microbiota but are also interested to see if this intervention could actually improve the infants’ phenotypes, like their neurodevelopment,” explains Professor Yan He, a principal investigator at the Division of Laboratory Medicine at Zhujiang Hospital and the Microbiome Medicine Center, SMU.

He is the lead author of a new, triple-blind collaborative study that explored the impact of vaginal seeding on a cohort of babies delivered via C-section at the Seventh Affiliated Hospital, SMU in China. The cohort of mothers and babies were divided into two groups: one where 32 newborns’ lips, skin and hands were rubbed with a gauze soaked in their mothers’ vaginal fluids, and 36 newborns that received a gauze soaked with saline. The researchers emphasize that safety tests were conducted to ensure that the mothers did not carry any infections, such as group B streptococcus or sexually transmitted diseases.

Clinical trial explores effectiveness of vaginal seeding on newborns

He and colleagues discovered that, after six weeks, newborns receiving vaginal fluids presented with more gut bacteria that was found in the maternal vaginal fluid than newborns receiving saline. This implies that the bacteria were capable of reaching and colonizing the newborns’ guts from the areas of their body that were rubbed with the soaked gauze. This cohort also presented with more mature gut bacteria after six weeks, resembling the gut microbiome composition of babies delivered vaginally.

Triple-blind randomized controlled trial shows that maternal vaginal microbiota seeding has positive effects. Credit: Cell Host & Microbe/He et al.

Possible impacts on neurodevelopment?

To assess whether the vaginal seeding intervention affected the newborns’ phenotypes, He and team evaluated their neurodevelopment at three and six months of age via a questionnaire completed by the babies’ mothers. They were asked whether their child could produce simple sounds or engaged in movements such as crawling. Babies in the vaginal seeding cohort’s scores were significantly higher at three and six months of age, again, comparable to those of vaginally delivered babies. However, the self-report approach to collecting this data must be considered as a possible limitation to its validity.

In the paper, the research team suggest that the finding of more mature bacteria in the guts of babies that underwent vaginal seeding may be linked to the improved neurodevelopment scores: “The maturation of the gut microbiota in newborns is an essential feature for early microbiota development. Previous observational studies have revealed that the abundances of Escherichia, Bifidobacterium and Lactobacillus in C-section-delivered neonates were lower than those in vaginally delivered neonates and increased with gut microbiota maturation,” they write.

“In contrast, some pathobionts, such as Staphylococcus and Klebsiella, decreased over time. These aging-associated gut microbial taxa were also reported to be associated with neurodevelopment during infancy, including temperament traits, cognitive and motor development and brain damage. In the present study, we not only recaptured a gut microbial maturation trajectory in infants delivered by C-section, but also found that VMT could accelerate this process,” they add. 

How early gut bacteria are capable of affecting neurodevelopment remains unknown. “There is some indirect evidence that shows some microbial metabolites are related to conditions,” He says. Babies who received vaginal seeding presented with increased levels of indolelactic acid – a metabolite produced by several Clostridium bacteria species – in their poop. Lower levels of this same metabolite have been identified in individuals with neurodegenerative diseases, including Parkinson’s disease and Alzheimer’s disease, the researchers say.

Larger clinical trials to come next

“We’re hoping this study can provide some leads to future research in this field. We want to know if vaginal microbiota seeding has the potential to reduce the risk of neurodevelopmental disorders in children, such as ADHD, ASD, and intellectual disabilities,” He notes. The researchers are planning longer-term clinical research studies recruiting larger sample cohorts. “It is somewhat like fecal microbiota transplantation. We need more data to understand this intervention and make it more precise. We may eventually uncover what exactly is beneficial in maternal vaginal microbiota, which could enable us to design therapeutics for all infants born via C-section in the future,” He concludes.

The research team emphasize that there were no severe adverse events that occurred in the trial.

Reference: Zhou L, Qiu W, Wang J, et al. Effects of vaginal microbiota transfer on the neurodevelopment and microbiome of cesarean-born infants: A triple-blind randomized controlled trial. Cell Host & Microbiome. 2023. doi: 10.1016/j.chom.2023.05.022

This article is a rework of a press release issued by Southern Medical University. Material has been edited for length and content.