Effects of vaginal microbiota on in vitro fertilization outcomes in women with different infertility causes Original paper

What was studied?

This study examined how the vaginal microbiota—a community of microorganisms residing in the vaginal tract— affects in vitro fertilization (IVF) outcomes in women with various infertility causes. The focus keyphrase vaginal microbiota and IVF outcomes appears prominently because the researchers compared the microbial profiles of infertile women with polycystic ovary syndrome (PCOS) or tubal factor infertility (TFI) to fertile controls during the implantation window. Using 16S rRNA gene sequencing, they evaluated community structure, dominant species, and microbial signatures associated with pregnancy success or failure. The investigation focused on whether specific bacteria, including Lactobacillus iners, Lactobacillus jensenii, Prevotella bivia, Pseudomonas spp., and others, correlate with implantation success and could serve as microbial markers of IVF prognosis.

Who was studied?

The researchers evaluated 120 women, including 83 infertile patients (33 with PCOS, 50 with TFI) and 37 fertile controls whose samples were collected during natural ovulation. After exclusions, 77 infertile women underwent fresh embryo transfer and were categorized into pregnant (PCOS.P, TFI.P) and non-pregnant (PCOS.NP, TFI.NP) groups. Vaginal swabs were collected from all participants within the implantation window—either 24 hours before embryo transfer or 6–8 days after ovulation in controls. Participants varied modestly in BMI and hormone profiles, but these clinical factors did not significantly influence microbial patterns, allowing for a microbiome-focused interpretation of results.

Most important findings

Vaginal microbiota structures differed between PCOS, TFI, and fertile women, with Lactobacillus-dominant communities remaining the norm but varying by species. The most clinically relevant finding was the association between Lactobacillus iners dominance and IVF failure. Across infertility types, L. iners was more abundant in non-pregnant women, suggesting a less stable or protective vaginal environment. In contrast, L. jensenii appeared more favorable, being more represented in pregnant groups. Microbial diversity was slightly higher in pregnant women, but beta-diversity differences were not statistically significant. Both infertile groups showed specific microbial enrichments: PCOS women displayed greater abundance of Prevotella, Dialister, and Veillonellaceae, while TFI women showed higher Parvimonas and Peptostreptococcaceae. A consistent negative marker was the increased presence of Pseudomonadaceae, especially Pseudomonas spp., in non-pregnant women. Additionally, women with prior miscarriages or ectopic pregnancies exhibited reductions in Lactobacillus and increases in potentially pathogenic genera, emphasizing the link between historical reproductive outcomes and present microbial patterns.

Key implications

This study strengthens the evidence that vaginal microbiota composition directly influences IVF outcomes, with L. iners emerging as a potential microbial indicator of failed implantation. The findings support integrating pre-transfer microbiome assessment into ART workflows to optimize embryo transfer timing and personalize treatment based on infertility type. Elevated Pseudomonas or dysbiotic patterns may warrant targeted evaluation or clinical microbiome-modulating interventions. The work highlights the need for microbial signatures in clinical reproductive medicine and suggests that monitoring and modulating the vaginal ecosystem could materially improve IVF success rates.

Citation

Zhao H, Wang C, Rao MP, et al. Effects of vaginal microbiota on in vitro fertilization outcomes in women with different infertility causes. Microbiology Spectrum. 2025;13(3):e01255-24. doi:10.1128/spectrum.01255-24