It should be stressed that the evidence for a placental microbiome is controversial. Most studies supporting the existence of a placental microbiome lack the appropriate experimental controls, and it has been found that contamination is most likely responsible for reports of a placental microbiome.
The placental microbiome more closely resembles that of the oral microbiome than either the vaginal or rectal microbiome. Changes in the microbiome can result is disease.
In a healthy placental microbiome, the diversity of the species and genera is extensive. A change in the composition of the microbiota in the placenta is associated with excess gestational weight gain, and pre-term birth.
The placental microbiota varies between low birth weight infants and those infants with normal birth weights.
While bacteria are often found in the amniotic fluid of failed pregnancies, they are also found in particulate matter that is found in about 1% of healthy pregnancies.
In non-human animals, part of the microbiome is passed onto offspring even before the offspring are born. Bacteriologists assume that the same probably holds true for humans.
Future research may find that the microbiota of the female reproductive tract may be related to pregnancy, conception, and birth. Animal studies have been used to investigate the relationship between oral microbiota and the placental microbiota. Mice inoculated with species of oral bacteria demonstrated placental colonization soon afterwards.
Investigations into reproductive-associated microbiomes began around 1885 by Theodor Escherich. He wrote that meconium from the newborn was free of bacteria. This was interpreted as the uterine environment was sterile. Other investigations used sterile diapers for meconium collection. No bacteria were able to be cultured from the samples. Bacteria were detected and were directly proportional to the time between birth and the passage of meconium. A 1927 study demonstrated the presence of bacteria in the amniotic fluid of those that were in labor for longer than six hours.
^Schwiertz, Andreas; Rusch, Volker (2016). "A Short Definition of Terms". In Schwiertz, Andreas (ed.). Microbiota of the Human Body. Advances in Experimental Medicine and Biology. pp. 1–3. ISBN978-3-319-31248-4.
^Yarbrough VL, Winkle S, Herbst-Kralovetz MM (2015). "Antimicrobial peptides in the female reproductive tract: a critical component of the mucosal immune barrier with physiological and clinical implications". Human Reproduction Update. 21 (3): 353–77. doi:10.1093/humupd/dmu065. PMID25547201.
^Mor G, Kwon JY (2015). "Trophoblast-microbiome interaction: a new paradigm on immune regulation". American Journal of Obstetrics and Gynecology. 213 (4 Suppl): S131–7. doi:10.1016/j.ajog.2015.06.039. PMID26428492.
^ abcTodar, K. "Pathogenic E. coli". Online Textbook of Bacteriology. University of Wisconsin–Madison Department of Bacteriology. Retrieved 2007-11-30.