Preterm delivery (PTD) of babies is thought in some women to be associated with the development of vaginal infections. An imbalance in the bacteria normally present in the vagina and especially a lack of Lactobacillus species can develop into a condition known as bacterial vaginosis (BV), which is a risk factor for PTD. The use of antibiotics is the standard treatment, however concerns on its effectiveness in preventing PTB have been raised. Antibiotics not only eradicate the abnormal bacteria, but also the Lactobacillus. This randomised control trial of 129 women with BV aimed to determine the effect of vaginally applied lactobacilli on the restoration of normal bacteria in the vagina and the rate of PTD. The results showed that women who had a complete lack of Lactobacillus, the vaginal application of Lactobacillus casei rhamnosus, BV was improved and gestational age at delivery and birthweight were both significantly increased, although PTD rate was not. It was concluded that vaginally applied Lactobacillus may be of some benefit to women with BV during pregnancy. This study could be used by healthcare professionals to understand the importance of vaginal microbiota during pregnancy. However, this was a study of very small numbers of women and larger studies are needed before vaginally applied microbiota can be definitively recommended.