Genesis of intestinal flora in babies: where are we now?

Actu GP Naissance de la flore intestinale du bébé : où en est-on ?

Does microbial colonization begin in utero? A review published in the journal Nature summarizes the history of research and opinions on a controversial subject which has not yet yielded all its secrets.


Experts have long considered the uterus to be a completely sterile environment. This theory has been questioned for several years: a child’s flora could be developed during gestation. Scientific journalist Cassandra Willyard has published an article summarizing the major research and questions relating to a controversy triggered by the results of an American team in 2011: the researchers had then detected “good bacteria” in human placenta with no trace of an immune reaction. This discovery turned this potential fetal microbiota an integral part of pregnancy, capable of influencing the development of the immune system. This lets us glimpse a lead to the prevention of certain pathologies, in particular allergic conditions.

Placental transfer or amniotic infection?

The idea that the placenta can carry components of the developing flora was corroborated by the results of several international studies. Some had demonstrated the presence of bacterial DNA in the placenta; others had shown a difference between the vaginal microbiota of the mother and that of the child after birth, suggesting that microorganisms are transmitted through the blood. In return, skeptics emphasized that DNA does not make the bacterium: it may be used to characterize them, not to demonstrate their presence. Another hypothesis: the amniotic fluid could be “contaminated” before its ingestion by the baby, who would develop his/her own intestinal microbiota in this way. This is reflected in the baby’s first bowel movements, which vary depending on whether the child is born prematurely or at term. There is no certainty, but according to the researchers involved, the assumptions are becoming stronger.

A still lively controversy

The fetal microbiota theory is disparaged by some scientists and is still precarious, deplores the journalist, especially as numerous placental analyses performed by different teams have not revealed any trace of microbes. But these results do not necessarily confirm that the environment is sterile, as low concentrations of microorganisms are difficult to detect. Consequently, for the moment there is no consensus. Although some scientists rely on the existence of germ-free mice strains to confirm the sterility of the uterine environment, most experts do not exclude a possible colonization during pregnancy. The subject remains open, studies continue, and funding is regularly allocated to drive forward this emerging research area, which generates both enthusiasm and skepticism.



C. Willyard. Baby’s first bacteria. Nature, vol. 553, 18 january 2018.