Placental Microbiome and Its Role in Preterm Birth

Despite the well-known fact that the placenta has long-term effects on maternal and fetal health, the placenta remains a poorly understood and understudied organ. Not only is the placenta a site of exchange of nutrients and blood and gases between the fetal and maternal systems, but it also performs critical metabolic functions for supporting fetal development and maintaining maternal-fetal tolerance. It is also abundantly clear that impairment of placental function leads to severe pregnancy complications, including preterm birth (PTB), a significant cause of perinatal mortality and morbidity worldwide. Understanding the causes of PTB and other adverse outcomes is clearly essential for the development of effective methods of prevention and treatment. We focus our review of one major known cause of PTB, namely, infection. We also introduce a new and somewhat unexpected factor(s) that may well affect PTB and every aspect of placental biology and function: the placental microbiome. We discuss the implications of the placenta housing a microbial biomass for PTB and the effect of maternal microbiomes at various niches for fetal colonization and health outcomes. We suggest that the placenta is an integral part of the pipeline for microbe-powered driver of fetal destiny.