# The predictive value of a multivariable model based on vaginal Lactobacillus relative abundance and microecological features at 24 weeks gestation and before delivery in spontaneous preterm birth: A Prospective cohort study

## TL;DR

This study finds that lower levels of Lactobacillus in the vagina during pregnancy are linked to a higher risk of spontaneous preterm birth, suggesting early microbiome checks could help identify at-risk women.

## Contribution

The study introduces a multivariable model using vaginal Lactobacillus abundance and microecological features to predict spontaneous preterm birth.

## Key findings

- Lower Lactobacillus relative abundance at 24 weeks gestation is independently associated with increased risk of spontaneous preterm birth.
- Combining vaginal microbiome data with clinical factors improves prediction of preterm birth (AUC = 0.775).
- Women with higher Lactobacillus levels at 24 weeks and before delivery have significantly higher chances of term delivery.

## Abstract

Vaginal microecological imbalance, particularly reduced Lactobacillus dominance, is a significant risk factor for spontaneous preterm birth (sPTB).However, the predictive value of microbial composition, pathogen colonization, and vaginal inflammation biomarkers at different pregnancy stages remains unclear. This study aims to evaluate the predictive potential of vaginal microecology at 24 weeks of gestation and before delivery for spontaneous preterm birth.

This was a prospective multicenter cohort study. Vaginal swabs were collected at 24 weeks of gestation and before delivery to assess Lactobacillus relative abundance(LRA), pathogen colonization, and biochemical markers (pH, hydrogen peroxide, leukocyte esterase, and sialidase). Multivariable logistic regression models, ROC curves, and Kaplan-Meier survival analysis were used to identify predictors of spontaneous preterm birth.

At 24 weeks of gestation, the preterm group showed significantly lower Lactobacillus relative abundance, higher AV and Nugent scores, and higher vaginal pH. Logistic regression revealed that an increase in Lactobacillus relative abundance(LRA) was negatively associated with sPTB (OR = 0.97, 95% CI = 0.96–0.98, P < 0.001), while higher parity (OR = 2.28, 95% CI = 1.56–3.32, P < 0.001) and a history of late miscarriage/preterm birth (OR = 6.96, 95% CI = 2.77–17.47, P < 0.001) increased the risk. Lactobacillus relative abundance(LRA) below 57.5% was linked to increased preterm birth risk in univariate analysis, but this was no longer significant after multivariable adjustment. Parity, late miscarriage/preterm birth history, vaginal pH > 4.5, and GBS positivity remained independent risk factors (AUC = 0.775). Kaplan-Meier survival analysis showed that women with LRA > 72.5% at 24 weeks and LRA > 57.5% before delivery had significantly higher term delivery probabilities (log-rank P < 0.001).

At 24 weeks, reduced vaginal LRA is an independent predictor of spontaneous preterm birth. Early vaginal microbiome assessment, combined with clinical features, can help identify high-risk pregnant women and improve outcomes.