The vaginal microbiome is closely linked to in vitro fertilization (IVF) outcomes in women with infertility. This study analyzed the vaginal microbiota of 1411 infertile women, including 1255 undergoing embryo transplantation, and found that a moderate abundance of Lactobacillus species, particularly Lactobacillus crispatus and Lactobacillus iners (~80%), is more beneficial for pregnancy than higher or lower abundances. A moderate Lactobacillus abundance was associated with higher pregnancy rates (54.35% for I-B and 57.73% for III-B) compared to higher abundances (44.81% for I-A and 51.06% for III-A). The community state type (CST) IV-B, which contains a high to moderate relative abundance of Gardnerella vaginalis, showed a similar pregnancy rate (48.09%) to I-A and III-A, with pregnant women in this CST having higher Lactobacillus abundance. Metagenome analysis revealed that nonpregnant women had more antibiotic resistance genes and higher levels of Proteobacteria and Firmicutes. Differences in vaginal microbiota among women with different infertility types suggest that vaginal microbes could be used to detect infertility and improve IVF outcomes. The study also found that certain bacterial genera, such as Lactobacillus, were negatively correlated with other genera, while Gardnerella and Prevotella were positively correlated with others. At the species level, L. iners and L. crispatus were negatively correlated with most other species. The study highlights the importance of vaginal microbiota in reproductive health and IVF outcomes, suggesting that a balanced Lactobacillus abundance is crucial for successful IVF. The findings may help develop strategies for predicting and managing vaginal microbiota to improve IVF outcomes.The vaginal microbiome is closely linked to in vitro fertilization (IVF) outcomes in women with infertility. This study analyzed the vaginal microbiota of 1411 infertile women, including 1255 undergoing embryo transplantation, and found that a moderate abundance of Lactobacillus species, particularly Lactobacillus crispatus and Lactobacillus iners (~80%), is more beneficial for pregnancy than higher or lower abundances. A moderate Lactobacillus abundance was associated with higher pregnancy rates (54.35% for I-B and 57.73% for III-B) compared to higher abundances (44.81% for I-A and 51.06% for III-A). The community state type (CST) IV-B, which contains a high to moderate relative abundance of Gardnerella vaginalis, showed a similar pregnancy rate (48.09%) to I-A and III-A, with pregnant women in this CST having higher Lactobacillus abundance. Metagenome analysis revealed that nonpregnant women had more antibiotic resistance genes and higher levels of Proteobacteria and Firmicutes. Differences in vaginal microbiota among women with different infertility types suggest that vaginal microbes could be used to detect infertility and improve IVF outcomes. The study also found that certain bacterial genera, such as Lactobacillus, were negatively correlated with other genera, while Gardnerella and Prevotella were positively correlated with others. At the species level, L. iners and L. crispatus were negatively correlated with most other species. The study highlights the importance of vaginal microbiota in reproductive health and IVF outcomes, suggesting that a balanced Lactobacillus abundance is crucial for successful IVF. The findings may help develop strategies for predicting and managing vaginal microbiota to improve IVF outcomes.