Vaginal Nugent Lactobacillus morphotype score and endometrial pathogen detection: a two-centre retrospective study.

INTRODUCTION

This two-centre retrospective observational study investigated whether the vaginal Nugent Lactobacillus morphotype score (LMS) is associated with endometrial pathogen detection and intrauterine Lactobacillus abundance in women with infertility.

METHODS

The study included 282 women (Centre A, n = 92; Centre B, n = 190) who underwent simultaneous vaginal Nugent scoring and endometrial quantitative PCR between March and December 2025. Women who had used antibiotics within one month or any probiotics before testing were excluded. Associations were assessed by Spearman rank correlation and by multivariable logistic regression adjusted for centre, age, BMI, and recurrent implantation failure.

RESULTS

LMS was positively associated with endometrial pathogen detection (ρ = +0.229, p < 0.001). After adjustment for centre, age, BMI, and recurrent implantation failure, each one-point increase in LMS was associated with higher odds of pathogen detection (adjusted OR 1.40, 95% CI 1.17-1.68; p < 0.001). However, discriminatory performance was limited (AUC 0.636, 95% CI 0.567-0.705), and pathogen detection remained 23.3% at LMS 0. LMS was negatively correlated with total intrauterine Lactobacillus (ρ = -0.488, p < 0.001) and L. crispatus (ρ = -0.411, p < 0.001). All 56 women with LMS 4 were L. crispatus-negative; however, when LMS 4 was treated as a positive result, sensitivity for L. crispatus absence was only 30.8%.

DISCUSSION: Vaginal LMS is an associated preliminary non-invasive indicator, but it cannot substitute for direct endometrial assessment or reliably exclude endometrial pathogen detection.