CHAPTER 5 The relation of the vaginal microbiota to early pregnancy development during In Vitro Fertilization treatment – A meta-analysis

Study question: of the vaginal microbiota composition on early pregnancy rates after IVF treatment? Summary answer: Women with an abnormal vaginal microbiota are roughly 1.4 times less likely to have a successful early pregnancy development after IVF treatment when compared to women with normal microbiota. What is known already: An abnormal vaginal microbiota composition has been shown to lead to pre-term births, miscarriage, and problems with conceiving. Studies have suggested that dysbiosis reduces successful early pregnancy development during IVF. However, Study design, size, duration: A systematic review was performed using the Medline and EMBASE databases, using search terms for healthy vaginal microbiota, abnormal vaginal microbiota, fertility and pregnancy. Participants/materials, setting, methods: The search resulted in six included articles. Of these, all six were used for further meta-analysis. Main results and the role of chance: We found a correlation between abnormal vaginal microbiota and lower rates of early pregnancy development after IVF treatment (OR = 0.70, 95% CI = 0.49 0.99). One study showed the reverse correlation. Limitations, reasons for caution: Heterogeneity between study methodologies in various forms was found. Heterogeneity in primary outcomes as well as IVF methodology characteristics and sampling times is likely to affect study outcomes. We press for caution and ask researchers and readers of the literature to pay special attention to the possible confounding factors that can effect study outcomes, as they appear prevalent. Study funding/competing interest(s): N/A. Trial registration number: PROSPERO number: CRD42018093149