Microbiota establishment: an in utero colonization decisive for future health?

Some diseases seem to have a developmental origin. Today, the microbiota is recognized as a determinant in health and diseases and one important step is its establishment in the neonate. Some variations in its composition including an imbalance (also called dysbiosis) have been associated to several pathologies. Recent studies suggest a bacterial colonization in the non-pregnant uterus, in the amniotic fluid and in the placenta, which were previously thought sterile. So, during developmental phases, the fetus could have encounter bacteria in utero. These bacteria could contribute to its microbiota establishment before parturition and therefore before the encounter with all microorganisms from vaginal, fecal and cutaneous microbiotas according to the delivery mode. However, studies stating the existence of such in utero microbiota, characterized by a low biomass, are somewhat disputed.