Objectives: The aims of this study were to describe the course of vulvovaginal candidiasis (VVC), trichomoniasis, and bacterial vaginosis (BV) in pregnancy and to explore the association between these longitudinal changes and pregnancy outcomes. Methods: A total of 793 pregnant women were enrolled at the first trimester of pregnancy and were followed prospectively twice at the second and third trimester. VVC, trichomoniasis, and BV were evaluated at each trimester of pregnancy. Results were evaluated for trends of these three diseases and the association between these changes of trends and pregnancy outcomes. Results: The trend of negative at all three time points was dominant for all three diseases compared with trend of positive throughout pregnancy was the most rare. In addition, for VVC, a trend toward positive can't be ignored (7.5%). However, for BV, the distribution of other three trends (trend negative, trend positive, status random) were basically the same. Different trends of these three diseases were not associated with adverse pregnancy outcomes, with the exception of women who had a trend of BV positive throughout pregnancy were more likely to suffer from amniotic fluid infection (AFI) compared with women who were negative at all three time points (p = .016, OR: 17.29, 95% CI: 1.70-175.54). Conclusions: In this population, the trend of negative throughout pregnancy was dominant for all three diseases compared with few women were positive across their pregnancy. BV may be associated with AFI during pregnancy.