Evidence shows that the presence of uterine 16S rRNA is not only the result of sampling or analysis errors and deserves to be acknowledged.Concept of the sterile endometrium, and the uterine compartment in general, is outworn, although the true core uterine microbiome still needs to be assessed. Functional studies are needed to elucidate the physiological importance of the microbiome in fertility. The challenge of studying reproductive immunology and the microbiota involved is that research on all of the different aspects is still in its infancy; microbiome, immunity, endocrinology in pregnancy, and placental and fetal development need to be studied together to obtain a more comprehensive overview.