The composition of the vaginal microbiome is associated with pregnancy complications. However, it’s unclear whether the microbiome of the uterine lining (endometrium) is related to specific outcomes in patients undergoing assisted reproductive technology (ART). To find out, researchers recently analyzed the association of the endometrial microbiome with live birth, biochemical pregnancy, clinical miscarriage, and lack of pregnancy in 342 ethnically diverse infertile patients across 3 continents. 16S rRNA sequencing of endometrial fluid and biopsies before embryo transfer revealed that dysbiosis was related to poor reproductive outcomes. Specifically, increased proportions of pathogenic bacteria such as Gardnerella, Streptococcus, Atopobium, and Klebsiella were associated with a lack of live birth, while dominance of Lactobacillus bacteria was associated with live birth. Lactobacillus may have helped prevent pathogens from taking up residence rather than exerting direct beneficial effects, as an absence of any bacteria also appeared to be linked to good outcomes. Although further studies are needed to clarify the mechanisms, the findings suggest that the endometrial microbiota composition prior to embryo transfer is a helpful biomarker that can be used to predict and improve the outcomes of assisted reproduction.