To assess the vaginal microbiome throughout full-term uncomplicated pregnancy, a longitudinal study was designed for 12 healthy women who had prepared to become pregnant and then delivered at term (38-42 weeks) without complications. The vaginal microbial community was studied at pre-pregnancy, 8-12, 24-28, 37-38 weeks of gestation, and puerperium, using hypervariable tag sequencing of the V3-V4 region of the 16S rRNA gene. Sequencing produced approximately 10 million reads on the Illumina MiSeq. Members of the Firmicutes phyla were prevailing before and during pregnancy periods, and the proportion was quite as Proteobacteria until puerperium. Lactobacillus genus was abundant before and during pregnancy, but post-delivery vaginal microflora variety turned diverse. The species-level analysis revealed that a healthy vaginal microbiome before or during pregnancy was prominently dominated by Lactobacillus crispatus. Furthermore, PCoA analysis revealed for differences in the bacterial community composition between the two levels of Lactobacillus species in pre-pregnancy and pregnancy period (PC1 contribution of 58.46%, PC3 contribution of 8.64%). Based on the taxonomic and PCoA analysis, we found that L. crispatus was dominant in the vaginal microflora of healthy women before or during pregnancy, but at the puerperium, the status changed leading to decreased abundance of protective Lactobacillus species that made vaginal micro-ecological barrier vulnerable to diseases. Additionally, vaginal pH was an important environmental property affecting the vaginal microbial community. © 2020 The Author(s).