The maternal microbiome and pregnancy outcomes.

Alterations of the human microbiome are a known characteristic of various inflammatory disease states and have been linked to spontaneous preterm birth and other adverse pregnancy outcomes. Recent advances in metagenomic research has proven that the placenta harbors its own rich diverse microbiome, even in clinically healthy pregnancies, and preterm birth may be a result of hematogenous infection rather than exclusively ascending infection as previously hypothesized. In this review, we describe the microbiome in healthy nongravid and gravid women to contrast it with the alterations of the microbiome associated with spontaneous preterm birth. We also discuss the importance of host gene-environment interactions and the potential for microbiota-specific targeted therapies to reduce the risk of adverse pregnancy outcomes.