Dynamic changes in the pregnancy microbiome and their role in preterm birth

Preterm birth (PTB) remains a leading cause of neonatal morbidity and mortality worldwide, posing significant challenges to maternal and child health. Recent advances have highlighted the critical role of the maternal microbiome-encompassing vaginal, gut, and oral microbial communities-n influencing pregnancy outcomes. This review comprehensively summarizes the dynamic changes of the pregnancy microbiome and elucidates its association with PTB. During healthy pregnancy, the vaginal microbiome is dominated by Lactobacillus with low diversity, while dysbiosis with fewer Lactobacilli and more anaerobes increases PTB risk. The gut microbiome also shifts, with reduced beneficial bacteria and more pro-inflammatory species linked to adverse outcomes. Changes in the oral microbiome and periodontal disease can promote systemic inflammation contributing to PTB. Microbial imbalance may trigger PTB through inflammation, immune changes, and microbial spread to the uterus. Targeting the microbiome via probiotics shows promise, but more clinical studies are needed. This review highlights the pregnancy microbiome as a key biomarker and intervention target to reduce PTB.