Are human fetuses bathing in bacteria?

Researchers confirmed the presence of bacterial DNA in amniotic liquid of pregnant women and in the gastrointestinal tract of the fetus. These microorganisms could impact the in utero development, especially that of the baby’s immune system.

Created 17 September 2019
Updated 14 May 2024
Actu GP : Le fœtus humain en plein bain bactérien ?

About this article

Created 17 September 2019
Updated 14 May 2024

The fetus grows in a sterile environment”. This belief–formerly unshakable–is called into question as experts have identified traces of bacterial DNA in the amniotic liquid and (sidenote: Meconium Earliest “stool” of the newborn, containing the amniotic liquid absorbed in utero. The meconium helps identify microorganisms lining the gastrointestinal tract of the fetus.
, both representative of the intrauterine environment. Identifying the presence of microorganisms is all the more important since they impact the development of the child’s immunity and build their microbiota.

Cutting-edge DNA analysis

In order to confirm the existence of microbes and identify them, Australian researchers analyzed the bacterial DNA present in the amniotic liquid of 50 pregnant women and that of the meconium of their children born via elective c-section. A specific procedure was able to minimize the risk of contamination (during a manipulation for instance) which might skew the results.

Bacteria everywhere...

DNA analyses finally revealed bacteria in a large majority of studied samples, sometimes common to both environments. One non-pathogenic species is dominant in the meconium: Pelomonas puraquae, although the reason why has not been explained (external contamination was considered, despite the measures taken). For its part, amniotic liquid contains DNA from skin commensal (“regular”) bacteria, mainly Propionibacterium acnes and staphylococci. Beneficial molecules produced by bacteria were also found in the meconium, especially short-chain fatty acids, known for their protective effects on health. All these findings show that fetal environment is not sterile and that the composition of its “microbiota” could impact the future health of the baby.

Old sources


L. Stinson, M. Boyce, M. Payne, et al. The Not-so-Sterile Womb: Evidence That the Human Fetus Is Exposed to Bacteria Prior to Birth. Front Microbiol. 10 :1024. 2019

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