Aim: To determine the diversity and stability of cultured vaginal lactobacilli in a multi-ethnic population of pregnant women. Methods and Results: A single-centre, prospective, cohort study was performed in a tertiary perinatal centre in East London, UK. Self-collected vaginal swabs at 13 and 20 weeks gestation were obtained from women attending for routine antenatal care and cultured for lactobacilli. In women who provided both swabs, 37 of 203 (18%) had no lactobacilli cultured at either time. Only 53 (26%) had the same species at both times. Black women were less likely to have lactobacilli cultured at 13 weeks (P = 0.014), and Black and Asian women were less likely to have lactobacilli cultured at 20 weeks (P = 0.002) compared with those in the White and Other groups. Conclusions: Significant differences exist between ethnic groups in the carriage and stability of vaginal lactobacilli. Significance and Impact of the Study: These differences have implications for the design of interventions aimed at normalizing the vaginal microbiota in pregnant women.