Effect of Waiting Period on Initial Adverse Vaginal Microbiome Composition in IVF-ICSI Patients

<b>Background/Objectives</b>: In this observational prospective cohort study, conducted at the Fertility Centre of the University Hospital, Duesseldorf Germany, the spontaneous reversal capacity and the effect of waiting time on an adverse vaginal microbiome profile in subfertile patients were investigated. <b>Methods</b>: Vaginal swabs of 76 patients were obtained before starting a fertility treatment using a commercially available test to perform a microbiome analysis. Patients with a favorable microbiome profile ("medium" or "high profile") according to the manufacturer's algorithm proceeded with the fertility treatment. Patients with an unfavorable microbiome profile ("low profile") postponed their fertility treatment and were sampled up to four times in each successive cycle or until a shift to a more favorable profile was detected. <b>Results</b>: Initially, 54/76 subjects had a high or medium profile and 23/76 had a low profile. Within 3 months, 75% of patients with an initial low profile shifted to a more favorable profile (7/23 dropouts). The presence of <i>Lactobacillus crispatus</i> in the initial sample was associated with a higher likelihood of a spontaneous shift to a more favorable profile. <b>Conclusions</b>: The vaginal microbiome is subject to strong fluctuations. Even an unfavorable microbiome profile can develop into a favorable microbiome profile within a few months without treatment.