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.