Background Recurrent vulvovaginal candidiasis (RVVC) and pelvic inflammatory disease (PID) are two of the most common infectious disorders in women’s reproductive health, frequently resulting in chronic discomfort and infertility. Both conditions share underlying mechanisms of microbial dysbiosis and immune-mediated inflammation. This study aimed to evaluate the efficacy of probiotics in preventing RVVC recurrence and to explore the correlation between PID and tubal infertility (TFI), emphasizing the role of the genital tract microbiome in reproductive outcomes. Methods A prospective dual-center study was conducted between January 2021 and December 2023 at National Taiwan University Hospital and Chang Gung Memorial Hospital.

1. A randomized, double-blind, placebo-controlled trial (n=200) assessing oral and intravaginal Lactobacillus rhamnosus GR-1 and L. reuteri RC-14 as adjuncts to antifungal therapy in women with RVVC. 2. A case-control study (n=250; 125 TFI cases, 125 fertile controls) investigating prior PID history, Chlamydia trachomatis seropositivity, and microbial imbalance as predictors of tubal damage. Clinical symptoms, vaginal pH, microbial load, and 16S rRNA microbiome composition were analyzed. Multivariate and correlation analyses identified risk factors for recurrence and infertility. Results In the RVVC trial, probiotic supplementation reduced recurrence rates (19% vs 44%; p<0.001) and prolonged recurrence-free survival. Vaginal Lactobacillus counts and Shannon diversity index significantly increased in the probiotic group. In the PID study, history of PID (aOR 3.62, 95% CI 1.84–7.10) and positive C. trachomatis IgG (aOR 3.34, 95% CI 1.52–7.32) were strongly associated with TFI. Microbiome analysis showed anaerobe-dominant flora and reduced Lactobacillus crispatus abundance in infertile women. The number of PID episodes correlated with tubal damage severity (r = 0.62, p<0.001). No major adverse events were reported. Conclusions Probiotic therapy effectively reduced recurrent vulvovaginal candidiasis and restored vaginal eubiosis, while prior PID—particularly chlamydial infection—was a significant determinant of tubal infertility. Findings highlight a continuum of genital tract dysbiosis linking lower tract infection with upper tract inflammation. Microbiome-centered interventions such as targeted probiotic therapy may represent a novel approach to both infection prevention and fertility preservation among reproductive-age women in Taiwan.