Compared to other human microbiota, vaginal microbiota is fairly simple with low bacterial diversity and high relative abundance of Lactobacillus species. Lactobacillus dominance is even more pronounced during pregnancy. Genetic factors, such as ethnicity, along with environmental, individual and lifestyle factors all have an impact on vaginal microbiota composition. The composition of the vaginal microbiota appears to play an important role in pregnancy as recent studies have linked it to adverse obstetric outcomes such as preterm birth, a leading cause of neonatal morbidity and mortality worldwide. However, the same vaginal microbiota does not seem to cause the same response in all women, calling for future research to fully understand the complex host-microbiota interplay in normal and complicated pregnancies.