Ligilactobacillus salivarius CECT5713 Increases Term Pregnancies in Women with Infertility of Unknown Origin: A Randomized, Triple-Blind, Placebo-Controlled Trial

Abstract

Background/Objectives: Unexplained infertility is a worldwide problem affecting a significant proportion of couples of reproductive age. Recent studies suggest that alterations in the vaginal microbiota are related to female infertility, while supplementation with some probiotic strains has been shown to improve pregnancy rates in couples experiencing this problem. This study aimed to evaluate the impact of oral administration of Ligilactobacillus salivarius CECT5713 on pregnancy success rates in couples with unexplained infertility prior to in vitro fertilization (IVF). Methods: Seventy couples were randomized to receive either a placebo or a probiotic intervention (one capsule per day containing an excipient only or 3 × 10⁹ viable cells of L. salivarius CECT5713 plus an excipient, respectively); 57 couples completed the study. Baseline data on demographics, health status (including gynecological and reproductive history), and lifestyle habits were collected. Vaginal swabs and semen samples were obtained from each couple before the intervention and immediately prior to IVF or upon confirmed pregnancy and were analyzed for microbiological (using both culture-dependent and -independent methods) and immunological profiles. Results: Oral administration of L. salivarius CECT5713 in couples with unexplained infertility scheduled for IVF resulted in a significantly higher pregnancy success rate (48.1%) compared to the placebo group (20.0%) (one-tailed Chi-square test; p < 0.024). The probiotic intervention improved both vaginal and semen immunological profiles, with no substantial changes observed in their microbial composition. Conclusions: These preliminary findings support the potential of L. salivarius CECT5713 supplementation to enhance fertility outcomes in couples with unexplained infertility.

Keywords: Ligilactobacillus salivarius; TGFβ1; VEGF; assisted reproduction techniques; infertility; probiotics; semen microbiota; vaginal microbiota.

Figure 1

Flow diagram of distribution of participant couples during the trial according to CONSORT guidelines [27].

Figure 2

Metataxonomic analysis of vaginal exudates. Boxplots showing the alpha diversity of vaginal microbiota, measured by Shannon (A,C) and Simpson (B,D) indices, in women according to the intervention (placebo in upper graphs and probiotic in lower graphs), the sampling time point (Time 1, Time 2), and the primary outcome of the study (successful pregnancy or not). Wilcoxon rank-sum tests were used to compare the alpha diversity indices.

Figure 3

Change in the relative concentrations of (A) L. salivarius DNA (log₁₀ CFU/mL) and the immunological parameters (B) TGFβ1 and (C) VEGF (pg/mL) in the vaginal exudate samples after the intervention in the placebo and probiotic groups. A red square was drawn around women who failed to achieve pregnancy or experienced miscarriage, and a green square indicates women with a successful pregnancy. Colored bars above the graphs indicate the treatment group (blue for placebo and green for probiotic).

Figure 4

Metataxonomic analysis of semen samples. Boxplots showing the alpha diversity of semen microbiota, measured by Shannon (A,C) and Simpson (B,D) indices, according to the intervention (placebo in upper graphs and probiotic in lower graphs), the sampling time point (Time 1, Time 2), and the primary outcome of the study (successful pregnancy or not). Wilcoxon rank-sum tests with Bonferroni-corrected p-values were used to compare the alpha diversity indices among the four subgroups defined by the placebo and probiotic groups at both time points and are shown at the lower right corner of the graphs (statistical significance was considered at p < 0.05). Significant differences in alpha diversity of semen samples within the probiotic group after the intervention (time 2) between couples achieving successful pregnancy and those who did not are indicated in the upper right corner of the graphs for the probiotic group.