Biogeographical effect on the diversity of vaginal microbiome in preterm birth: A systematic review and meta-analysis

Women of European Ancestry are more likely to harbor a Lactobacillus-dominated microbiome that supports healthy pregnancy progression compared to women of African descent who are more likely to experience preterm birth due to a diverse microbial profile. However, to date, many of these studies linking a diverse vaginal profile to adverse pregnancy outcomes in women of African ancestry are commonly focused on Blacks in Westernized populations. To bridge this gap, a comparative systematic review and meta-analysis were performed by searching PubMed, Web of Science, EMBASE, and Cochrane Library databases. A total of 40 studies assessing the vaginal microbiome and preterm birth using molecular-based techniques were selected for full-text review. After extensively analyzing these studies for experimental design, the method applied, clinical characteristics, and geographical location, only two articles fulfilled the inclusion criteria for meta-analysis. A meta-analysis was conducted by merging two studies comprising 217 samples from 115 pregnant women of African descent. Taxon analysis of vaginal profiles shows that Nigerian women had a significantly higher abundance of Atopobium (q<0.05; permutation test), compared to African American (AA) women who were significantly more enriched with Sneathia (q<0.05; permutation test). The mean Alpha-diversity was not significantly different between the AA and Nigerian groups (3.3 ​± ​0.09 versus 2.9 ​± ​0.09, p ​= ​0.10) respectively. Vaginal communities of AA women were relatively unstable, only Ureaplasma parvum remained stable throughout pregnancy (p_ADF <0.001), whereas L. crispatus, L. iners, and Atopobium vaginae were relatively more stable over pregnancy (p_ADF <0.001) in Nigerian women. In summary, our study indicated that there are differences in the core vaginal microbiome composition in women of similar ethnicity in different geographical locations. Future work should focus on advancing precision medicine by understanding the microbiome from an individual perspective, independent of ethnicity.