Elevated Level of Fannyhessea vaginae Correlated with Implantation Outcomes in Women undergoing in vitro fertilization Treatment.

The vaginal microbiome plays a significant role in reproductive health. While maintaining a balanced vaginal microbiome is crucial for successful in vitro fertilization (IVF) outcomes, the specific bacteria associated with adverse outcomes may vary by region and are largely unknown. This study aims to investigate the bacterial profiles and their influence on embryo implantation, thereby supporting the development of microbiome-based therapies. One hundred women undergoing IVF provided vaginal swabs at three stages: oocyte retrieval, embryo transfer, and hCG pregnancy testing. An in-house 16S rRNA gene amplicon sequencing and bioinformatics pipeline was used to profile the vaginal microbiota. Bacterial communities were constructed, and the transitions across IVF stages were analyzed. We also used custom quantitative PCR assays to validate NGS results and provide species-level resolution for selected bacterial species. Unlike other regions where Lactobacillus crispatus predominates, we found that Lactobacillus iners is the main vaginal microbiota across all IVF stages in Taiwan. Nevertheless, significant shifts in bacterial community types were correlated with hormonal changes during IVF treatment. Importantly, while Lactobacillus levels didn't predict pregnancy success, higher levels of bacteria associated with bacterial vaginosis, particularly Fannyhessea vaginae, significantly correlated with implantation failure and early embryonic loss. The strong association between elevated F. vaginae levels and adverse implantation rate in Taiwanese women highlights the potential benefit of incorporating routine screening for this pathogen. Personalized microbiome interventions targeting F. vaginae may improve embryo implantation for women undergoing assisted reproductive technologies.