The vaginal microbiota and preterm birth: A systematic review

Vaginal microbiota is a dynamic community of bacteria, fungi, and viruses that colonize the lower genital tract. Changes in vaginal microbiota can result in obstetric complication. For example, a reduction in Lactobacilli can lead to bacterial vaginosis, which is associated with preterm birth. We performed a systematic review to investigate the association between vaginal microbiota composition during pregnancy and preterm birth risk. Scopus, Web of Science, PubMed databases were used to find published studies on the topic. The search period was between January 2014 and June 2024. A total of 2194 full research articles were screened, and finally, we included 14 full-research articles. Demographic factors, such as self-identified ethnicity, age, substance use, and gestational age, influence the vaginal microbiota were identified. The greatest diversity in the composition of the vaginal microbiota was found between the first and second trimesters of pregnancy. We found a decrease in L. crispatus, L. gasseri and L. jensenii population, with a relative increase in L. iners, which were associated with preterm birth. In addition, Ureaplasma, Mycoplasma, and Gardnerella species were associated with increased rates of preterm birth. An increase in cytokines (IL-1(3, IL-6, and MIP-1(3) and a decrease in (3-defensin-2 values also seem to influence the preterm birth onset. In summary, we identified multiple vaginal microbiota that were associated with changes in the risk of pre-term birth. Further studies should focus on demonstrating a causal relationship and identifying interventions to reduce the risk of preterm birth associated with changes in the vaginal microbiota.