Quantitative bacteriology of the vaginal flora during the menstrual cycle.

The vaginal bacteriology of 10 healthy asymptomatic women was assessed during the menstrual cycle. Samples were taken from the posterior vaginal fornix for quantitative analysis. There were no significant alterations in the total vaginal flora at different stages of the menstrual cycle. The mean number of species isolated per specimen declined from 4.6 in week 1 to 2.9 in week 4. This decline was not caused by a decrease in the occurrence or concentration of any one organism or group of organisms. The vaginal pH decreased from a mean of 6.6 in week 1 to 4.3 in week 4, this increased acidity could not be attributed to the action of lactobacilli as their total incidence or concentration did not change during the menstrual cycle.