<p><strong>BACKGROUND: </strong>Short cervix is a risk factor for preterm birth. Molecular drivers of short cervix remain elusive. Metabolites may function as mediators of pathologic processes.</p>

<p><strong>OBJECTIVES: </strong>We sought to determine if a distinct cervicovaginal metabolomic profile is associated with short cervix (&lt;25 mm) to unveil potential mechanisms by which premature cervical remodeling leads to short cervix.</p>

<p><strong>STUDY DESIGN: </strong>This was a secondary analysis of a completed prospective pregnancy cohort. Cervicovaginal fluid was obtained between 20-24 weeks' gestation. Participants selected for metabolomic profiling were frequency matched by birth outcome and cervicovaginal microbiota profile. This analysis included the 222 participants with cervical length measured. Short cervix was defined as &lt;25 mm as measured by transvaginal ultrasound. Unpaired t-tests were performed with a Bonferroni correction for multiple comparisons.</p>

<p><strong>RESULTS: </strong>There were 27 participants with short cervix and 195 with normal cervical length. Of the 637 metabolites detected, 26 differed between those with short cervix and normal cervical lengths; 22 were decreased, of which 21 belonged to the lipid metabolism pathway (all P&lt;7.85E-5). Diethanolamine, erythritol, progesterone and mannitol/sorbitol were increased in cases of short cervix. Among participants with a Lactobacillus-deficient microbiota, only diethanolamine and mannitol/sorbitol differed between short cervix (n=17) and normal cervical length (n=75), both increased.</p>

<p><strong>CONCLUSIONS: </strong>Short cervix is associated with decreased cervicovaginal lipid metabolites, particularly sphingolipids. This class of lipids stabilizes cell membranes and protects against environmental exposures. Increased diethanolamine, an immunostimulatory xenobiotic, is associated with short cervix. These observations begin to identify potential mechanisms by which modifiable environmental factors may invoke cell damage in the setting of biologic vulnerability, thus promoting premature cervical remodeling in spontaneous preterm birth.</p>

<p>Biomechanical and molecular processes of premature cervical remodeling preceding spontaneous preterm birth (sPTB) likely result from interactions between the cervicovaginal microbiota and host immune responses. A non-optimal cervicovaginal microbiota confers increased risk of sPTB. The cervicovaginal space is metabolically active in pregancy; microbiota can produce, modify, and degrade metabolites within this ecosystem. We establish that cervicovaginal metabolomic output clusters by microbial community in pregnancy among Black individuals, revealing increased metabolism within the amino acid and dipeptide pathways as hallmarks of a non-optimal microbiota. Few differences were detected in metabolomic profiles when stratified by birth outcome. The study raises the possibility that metabolites could distinguish women with greater risk of sPTB among those with similar cervicovaginal microbiota, and that metabolites within the amino acid and carbohydrate pathways may play a role in this distinction.</p>