Association of low progesterone levels and periodontal disease with threatened preterm labor

Periodontal disease has been reported to increase the risk of threatened preterm labor (TPL). However, studies analyzing the oral, vaginal, and rectal lumen commensal flora in women with TPL are limited. In this study, a total of 60 women were enrolled, including 30 with TPL and 30 without TPL. We assessed periodontal clinical parameters, salivary hormone levels, and the microbiome using next-generation sequencing. Probing pocket depth (PPD) and bleeding on probing were greater in the TPL than in the non-TPL group. The TPL group was associated with lower progesterone levels and an increase in PPD ≥ 4 mm. Significant differences in alpha diversity in only vaginal Faith's phylogenetic diversity, and significant differences in beta diversity at all sites were observed. ANCOM showed decreased Lactobacillales in the saliva and Bifidobacterium in the rectal lumen, and increased Staphylococcus in the oral cavity and vagina in the TPL group. The peptidoglycan synthesis pathway was significantly upregulated in the oral and vaginal tissues in the TPL group. Overall, the TPL group had lower progesterone levels and more severe periodontal disease; furthermore, the low progesterone levels in the TPL group were associated with oral and vaginal dysbiosis of the microbiota.