The study investigates the association between vaginal microbiota and reproductive outcomes in infertile women, focusing on the impact of *Lactobacillus* abundance on in vitro fertilization (IVF) success. The research involved 1411 individuals, including 1255 undergoing embryo transplantation. Using 16S rRNA gene sequencing, the study found that both too high and too low abundance of *Lactobacillus* were detrimental to pregnancy, with a moderate abundance of *Lactobacillus crispatus* and *Lactobacillus iners* (~80%) being beneficial. The results suggest that a balanced vaginal microbiome, particularly with moderate levels of these *Lactobacillus* species, may improve IVF outcomes. The study also explored the correlation between vaginal microbiota and various clinical and biochemical parameters, highlighting the importance of understanding the vaginal microbiome in reproductive health and assisted reproduction.The study investigates the association between vaginal microbiota and reproductive outcomes in infertile women, focusing on the impact of *Lactobacillus* abundance on in vitro fertilization (IVF) success. The research involved 1411 individuals, including 1255 undergoing embryo transplantation. Using 16S rRNA gene sequencing, the study found that both too high and too low abundance of *Lactobacillus* were detrimental to pregnancy, with a moderate abundance of *Lactobacillus crispatus* and *Lactobacillus iners* (~80%) being beneficial. The results suggest that a balanced vaginal microbiome, particularly with moderate levels of these *Lactobacillus* species, may improve IVF outcomes. The study also explored the correlation between vaginal microbiota and various clinical and biochemical parameters, highlighting the importance of understanding the vaginal microbiome in reproductive health and assisted reproduction.