The frequent shift to intermediate flora in preterm delivery cases after abnormal vaginal flora screening

The effect of screening and treatment for abnormal vaginal flora on the reduction of preterm deliveries remains controversial. We evaluated whether this screening and treatment reduces the preterm delivery rate for general-population pregnant women. Pregnant women of the Intervention group (n = 574) underwent the screening test and the treatment of vaginal metronidazole during the early second trimester, and those of the Control group (n = 1,161) did not. We compared the preterm delivery rate between these two groups. We also compared the profiles of vaginal flora of the preterm delivery cases with those of the pregnant women with a normal course. There was no significant difference in the preterm delivery rate between these two groups. However, in the preterm delivery cases, a frequent shift to intermediate flora was observed not before but after the screening in the Intervention group. This shift may explain why most of the previous studies failed in regard to the prevention of preterm deliveries.