It is unsure that from where and when fetal and placental microbiota comes from. May be microbes are passed from intestinal lumen of mother or from the vaginal track or from the oral cavity or from the urinary track, it is unknown mechanism. Microbes transfer towards fetus may from a hematogenous route and then from placenta.
Some literature shows that placental microflora has somehow similar composition as oral community. Placental microflora has an association with antenatal infections, pre term birth and excess weight gain of mother.Currently, hypothesis is based on ascending route microbe transmission which consists of vagina and dendritic cells of mother. As the Lactobacilli species are present in vagina so, the proofs bacteria derived vaginally are becomes much strong just because of abundance of Lactobacillus-dominant microbiota in the placenta too. During period of pregnancy and lactation bacterial translocation through diffusion in the blood is increased. Low numbers of bacteria from intestine and oral cavity are circulated through blood and then seed in the placenta. Oral bacteria are known as basic source of placental bacteria in currently published literature. Almost 50% bacterial DNA is detected from the tissues of placenta and it has its own microbiome which is different from oral and vaginal microbial communities. An individual which is suffered from severe chorioamnionitis has some changes in placental microbiome. Severe birth outcomes are due to these altered communities of bacteria. Another study which has less sample size shows different data as compared to this study. Its samples was also analyzed by molecular methods as 16S rRNA gene sequencing, showed microbial community which has similarity with tonsils and tongue microbiome than the vagina. Some microbial communities which consists ofAnaeromyxobacter,Burkholderia, Roseovarius andStreptosporangiumwas known as environmental microbiome previously are the genera which are altered in term and pre-term delivery. They found huge number ofUreaplasma spp and Fusobacterium nucleatum which are indirectly related with pregnancy duration. Another study also find these genus of bacteria which may be the reason for pre term birth, which shows its pathogenic role during pregnancy. Some literature shows presence ofPrevotella spp.,Sneathia sanguinegens,Gardnerella vaginalisandPeptostreptococcusspp.in the amniotic fluid and placenta of the women with immature delivery cases. Some bacterial strains Ureaplasma spp., Gardnerella spp., Sneathia spp.,Lachnospiraceae spp. andPrevotella spp. are also detected in short duration pregnancy cases, which are previously known as a cause for bacterial vaginosis.Ureaplasma sppand Gardnerellaspp. are present in placental tissues was also present in vaginas of women which delivered preterm. Smaller new born size is associated withSneathia sanguinegensandPeptostreptococcus anaerobious which were present in the placenta and vagina too.