The vaginal microbiota plays a critical role in the health of the female genital tract, and its composition contributes to gynecological disorders and infertility. Lactobacilli are the dominant species in the female genital tract: their production of lactic acid, hydrogen peroxide, and bacteriocins prevents the invasion and growth of pathogenic microorganisms. Several factors such as hormonal changes, age of reproduction, sexual practices, menstrual cycle, pregnancy, and antimicrobial drugs use can cause imbalance and dysbiosis of the vaginal microbiota. This review aims to highlight the impact of the vaginal microbiota in Assisted Reproductive Technology techniques (ART) and it examines the factors that influence the vaginal microbiota, the consequences of dysbiosis, and potential interventions to restore a healthy female genital tract.

Background and aims: Failure of the embryo to implant causes about three-fourths of lost pregnancies. Female genital tract microbiota has been associated to Assisted Reproductive Technologies (ART) outcomes. The objective of this study was to analyze the microbiota of human cervical swab and to correlate these findings with the ART outcomes. Materials and Methods: In this study, 88 cervical swabs were collected from women undergoing ART cycles, with various causes of infertility, at the beginning of the ART protocols. After microbial DNA extraction, V3–V4 variable regions of the 16S rRNA gene were amplified and sequenced on the Illumina MiSeq platform. PEnalized LOgistic Regression Analysis (PELORA) was performed to identify clusters of bacterial populations with differential abundances between patients with unfavorable and favorable pregnancy outcome groups, respectively. Results: We identified a core of microorganisms at lower taxonomic levels that were predictive of women’s pregnancy outcomes. Statistically significant differences were identified at species levels with Lactobacillus salivarius, Lactobacillus rhamnosus among others. Moreover the abundance of Lactobacillus crispatus and iners, respectively increased and decreased in favorable group as compared to unfavorable group, resulted within the core of microorganisms associated to positive ART outcome. Although the predominance of lactobacilli is generally considered to be advantageous for ART outcome, we found that also the presence of Bifidobacterium (together with the other lactobacilli) was more abundant in the favorable group. Discussion: Cervix is colonized by microorganisms which can play a role in ART outcomes as seen by an overall decrease in embryo attachment rates and pregnancy rates in both fertile and infertile women. If confirmed in a larger cohort, the abundance of these bacteria can be useful not only as a marker of unfavorable pregnancy outcome but also they may open the way to new interventional strategies based on genital tract microbiota manipulation in order to increase the pregnancy rates in woman undergoing assisted reproductive technologies.

Background and aims: Vaginal microbiomes have been classified into five different general categories, termed Community State Type (CSTs), with CST-III and CST-IV often associated with vaginal dysbiosis which makes women more prone to recurrent infections and assisted reproductive technology (ART) failure. Since a healthy microbiome is one of the key steps for successful reproduction, we investigated the impact of modulating the vaginal microbiota through the oral administration of probiotic formula consisting of a consortium of vaginal-specific lactobacilli and prebiotics (Personal Flora 2^®). Methods: We recruited 32 women who had previous failed IVF cycles and were scheduled to undergo ART. We examined the composition of the vaginal microbiota before and after oral probiotic supplementation using 16S ribosomal RNA (rRNA) sequencing technology. Results: Our data show a noticeable modulation of the vaginal microbiome upon probiotic supplementation. In particular, precision probiotic intervention lowers the species diversity, favoring the dominance of Lactobacillus (p = 0.015) and Bifidobacterium (p = 0.000) whilst decreasing the percentage of Atopobium (p = 0.003), Gardnerella (p = 0.022), and Prevotella (p = 0.000). Conclusions: Although CST-III and CST-IV are generally considered detrimental, gynecologists should not refrain from performing IVF in these women if they have been previously subjected to a consortium of precision probiotics treatments, as the administration of specific probiotics reduces the presence of pathogenic bacteria promoting the increase in lactobacilli associated with a healthy vaginal ecosystem, which could impact pregnancy success.