Effects of vaginal microbiota on <i>in vitro</i> fertilization outcomes in women with different infertility causesOriginal paper
Karen Pendergrass is a microbiome researcher specializing in microbiome-targeted interventions (MBTIs). She systematically analyzes scientific literature to identify microbial patterns, develop hypotheses, and validate interventions. As the founder of the Microbiome Signatures Database, she bridges microbiome research with clinical practice. In 2012, based on her own investigative research, she became the first documented case of FMT for Celiac Disease, four years before the first published case study.
Read MoreWhat was studied?
This study asked whether the vaginal microbiota before embryo transfer relates to in vitro fertilization (IVF) outcomes, and whether it differs by cause of infertility. Only about 30 to 35 percent of women conceive after a first IVF transfer. The design was a retrospective case-control study sampling the vagina during the implantation window. Bacteria were profiled by 16S ribosomal RNA gene sequencing of the V3-V4 regions. Women with polycystic ovary syndrome (PCOS) and tubal factor infertility (TFI) were compared with fertile controls, then split by pregnant and non-pregnant outcomes.
Who was studied?
The cohort was 83 infertile women undergoing IVF (33 with PCOS, 50 with TFI) and 37 fertile control women, at a reproductive center in Guiyang, China, recruited June to September 2023. Control samples were taken 6 to 8 days after ovulation; infertile women were sampled within 24 hours before embryo transfer, both within the implantation window. After exclusions, 77 women (32 PCOS, 45 TFI) underwent transfer. Of these, 31 achieved clinical pregnancy (10 PCOS and 21 TFI), and the rest were classified as non-pregnant.
What were the most important findings?
The vaginal community structure differed between PCOS and TFI groups (ANOSIM p = 0.02), though alpha diversity did not differ significantly. Lactobacillus was more abundant in the TFI group and Gardnerella-associated dysbiosis featured more in PCOS. Among the 77 women who had transfer, 13 pregnant women had Lactobacillus as the dominant species, while only 1 pregnant woman was dominated by Gardnerella. Among non-pregnant women, 28 were Lactobacillus-dominant and 1 Gardnerella-dominant. A higher pre-transfer abundance of Gardnerella, alongside Lactobacillus iners, was associated with non-pregnancy, marking it as a potential adverse factor for IVF success.
What are the greatest implications of this study?
The results suggest vaginal microbiota composition before embryo transfer may influence IVF outcomes, and that the community differs by infertility type. Assessing it could help optimize transfer timing. A vagina dominated by Gardnerella before transfer may signal a lower chance of pregnancy, supporting more personalized care by infertility cause. Because the study was retrospective and observational, it cannot prove causation. The single-center Chinese cohort was modest in size, and vaginal community differences by outcome did not always reach statistical significance.