Vaginal Lactobacillus spp. Dominance in Late Pregnancy and Neonatal Anthropometric Outcomes: A Prospective Observational Study

Background/Objectives: Vaginal microbiota is relevant to pregnancy, but evidence on neonatal anthropometry is mainly molecular and focused on pre-term birth. This study evaluated whether microscopy-based vaginal lactobacillary dominance in late pregnancy is associated with neonatal anthropometric measures after accounting for maternal and gestational determinants. Methods: This prospective observational study included 144 mother–newborn pairs recruited at a tertiary hospital in Romania between February and August 2025. Gram-stained smears were assessed for lactobacillary dominance, leukocyte density, and candidiasis; a composite vaginal indicator was derived. Outcomes were birth weight, length, and head circumference. Associations were assessed using correlation, adjusted regression, hierarchical models, and sensitivity analyses. Results: Lactobacillary dominance was not associated with birth weight or length in bivariate analyses, but correlated weakly with head circumference (ρ = 0.186, p = 0.025). In adjusted models, it was nominally associated with higher birth weight (B = 133.5 g, p = 0.043) and larger head circumference (B = 0.47 cm, p = 0.034), but not birth length; these associations did not remain significant after multiple-testing correction. Incremental explanatory contribution was modest (ΔR2 = 0.022 and 0.025), and associations attenuated after socioeconomic adjustment. Leukocyte density and candidiasis were not associated with outcomes; intermediate versus balanced vaginal status was associated with lower birth weight and head circumference in exploratory analyses. Conclusions: Routine microscopy-based lactobacillary dominance showed modest nominal associations with birth weight and head circumference, limited incremental explanatory value, and no robustness after multiplicity correction. These findings suggest a context-dependent association with limited clinical relevance.