Vaginal dysbiosis: the cause of certain cases of infertility?
With a birth rate exceeding 52%, in vitro fertilization (IVF) is the technique of choice for treating infertility. For some women, however, the transferred embryo fails to implant, preventing any hope of pregnancy. Might an imbalance in the vaginal microbiota be the cause?
Defined as the inability to conceive offspring despite frequent sexual intercourse over at least a year, infertility affects 8% to 12% of couples of childbearing age. While IVF has quickly emerged as the most effective treatment, some women fail to become pregnant due to recurrent implantation failure (RIF). Hormonal, vascular, or immune disorders have recently been blamed, but such disorders cannot explain all embryo implantation failures. Already linked to numerous gynecological diseases and pregnancy-related disorders, might imbalances in the vaginal microbiota be involved in IVF failure as well?
An unbalanced, lactobacilli-depleted microbiota
To test this hypothesis, the vaginal microbiota of 67 women who had previously attempted IVF was analyzed. Of these, 27 had experienced unexplained RIF and 40 had carried their pregnancy to term following a single treatment cycle. The results showed the women who had experienced an RIF to be suffering from vaginal dysbiosis, specifically a more diverse and abundant microbial flora, with more bacteria linked to various genital infections (bacterial vaginosis, vaginitis, urinary tract infections). Conversely, their vaginal microbiota was relatively less rich in lactobacilli. According to the authors, the pregnancy rate exceeded 72% where lactobacilli made up more than 90% of the vaginal microbiota and fell to 34% where this was not the case.
Will the risk of IVF failure soon be predictable?
Lastly, the RIF patients also had different levels of certain substances produced by the vaginal microbiota, in particular significantly fewer of the molecules necessary for the implantation and development of the embryo, with this scarcity directly correlated to the reduced abundance of lactobacilli. The authors believe that the composition of the vaginal microbiota, and particularly lactobacilli depletion, plays a key role in the recurrent embryo implantation failure. They hope these results will pave the way for the development of biomarkers capable of predicting the risk of RIF.
Fu M, Zhang X, Liang Y, Lin S, Qian W, Fan S. Alterations in Vaginal Microbiota and Associated Metabolome in Women with Recurrent Implantation Failure. mBio. 2020;11(3):e03242-19. Published 2020 Jun 2. doi:10.1128/mBio.03242-19