New evidence suggests a baby’s microbiome forms before birth
Research into the human microbiome over the past few years has suggested the trillions of bacteria living inside our guts may be playing a role in everything from cancer and autoimmune disease, to cognitive and mental health. But one persistent mystery has surrounded the development of a person’s specific microbiome. Exactly when does the microbiome begin to form? Is the womb and placenta a completely sterile environment, and bacteria is first seeded when a baby is born? Or can a mother transfer microbes to her child during pregnancy, with a fetal microbiome forming during gestation?
A fascinating new study is offering evidence to suggest the microbiome does indeed begin to develop in utero. The novel research, examining a number of human, and animal, mother-child pairs, proposes not only the existence of a fetal microbiome but suggests a dynamic fetal bacterial population with a composition that notably shifts in diversity from mid- to late-gestation.
Due to technical and ethical limitations, it has proved challenging for scientists to clearly ascertain whether a fetal microbiome develops during pregnancy. The new research first studied a number of human mother-child pairs by taking samples from the operating room at the time of cesarean delivery. Comparing a mother’s vaginal, placental, and fecal microbiota with her offspring’s oral and meconium microbiota, the researchers suggest newborn infants do possess a microbiome that hypothetically originates from in utero sources, and not merely due to contamination or exposure during the birthing process.
“Our study provides strong proof that a complex microbiome is transmitted from the mother to the fetus,” says Patrick Seed, senior author on the new study. “Unlike other studies relying only on next generation DNA sequencing, we validated our sequencing results with microscopy and culture techniques, to resolve a decades long controversy about the existence of a fetal microbiome.”
The second part of the study involved a more systematic examination of fetal microbiota in mouse models. At various points from mid- to late-gestation, the animals were studied under sterile conditions with samples genetically sequenced to uncover the presence of bacterial DNA. The results revealed a dynamic fetal microbiome, changing in composition throughout different phases of gestation.
“Establishing a dynamic microbiome in the fetus leads us to suspect that controlled exposure to microbes trains the developing immune system and metabolism,” says Seed. “We need more research to better understand the mechanisms involved and how we can intervene to improve children’s health at the start of life and beyond.”
Although the study comes to a confident conclusion that a complex and dynamic fetal microbiome does indeed exist, the debate will certainly be ongoing. The researchers do concede it is extraordinarily difficult to discern environmental contaminants when analyzing samples, but the study does clearly report a number of, “bacterial 16S rDNA signatures were identified in the placentas of women who underwent cesarean delivery without labor that could not be attributed to laboratory contamination.”
A recent study into the microbiome differences between babies born by cesarean and those born by vaginal delivery interestingly found a vaginally birthed baby’s microbiome comprised very little trace of a mother’s vaginal bacteria. This seemed to imply that the traditional hypothesis suggesting a baby’s microbiome is primarily seeded through contact with bacteria in the mother’s birth canal is wrong. This new research certainly adds weight to the proposal that certain bacteria may be transferred from a mother to a fetus through the placenta.
Seed notes that if his team’s work can be verified in larger human cohorts, it may be possible to promote fetal health and development during pregnancy by modulating a mother’s microbiome.
“Now we can pursue ways to boost the development of fetal immune system and metabolism by stimulating mom’s microbiome,” says Seed. “Our findings point to many promising opportunities for much earlier intervention to prevent future disease.”
The new research is published in the journal JCI Insight.