The role of uterine and vaginal microbiome affecting the outcomes of assisted reproductive technologies

Infertility is a high-priority medical and social issue, which prevalence reaches 15 %according to the World Health Organization. One of the methods for infertility treatment, which is often resorted to by sub-fertile couples, is the use of assisted reproductive technologies (ART). It is known that the microbiome of the uterine cavity and vagina can affect ART-related fertility potential. The normal vaginal microbiome is characterized by the dominance of Lactobacillus spp . representatives, which ensure the maintenance of optimal pH values and prevent pathogenic microbial penetration and multiplication. It is assumed that the normal endometrial microbiome is characterized by predominance of Lactobacillus spp ., but relevant studies are prominently heterogeneous. According to the current hypothesis, the dominance of Lactobacillus spp . and, particularly, Lactobacillus crispatus , in the vagina and uterine cavity is associated with favorable reproductive outcomes in ART programs. Recurrent implantation failures are related to spreading of opportunistic microflora in such niches. Nevertheless, some authors have reported no direct correlation between Lactobacillus spp . level, presence of opportunistic microorganisms and favorable outcomes of ART programs, which underlies a need to conduct further large-scale studies.