Vaginal, Cervical and Uterine pH in Women with Normal and Abnormal Vaginal Microbiota

Abstract

Introduction: Healthy women of reproductive age have a vaginal pH around 4.5, whereas little is known about pH in the upper genital tract. A shift in the vaginal microbiota may result in an elevated pH in the upper genital tract. This might contribute to decreased fertility and increased risk of preterm birth. Therefore, we aimed to measure pH in different compartments of the female genital tract in both nonpregnant and pregnant women, stratifying into a normal and abnormal vaginal microbiota.

Material and methods: In this descriptive study, we included 6 nonpregnant, 12 early-pregnant, and 8 term-pregnant women. A pH gradient was recorded with a flexible pH probe. An abnormal vaginal microbiota was diagnosed by a quantitative polymerase chain reaction technique for Atopobium vaginae; Sneathia sanguinegens; Leptotrichia amnionii; bacterial vaginosis-associated bacterium 1, 2, 3, and TM7; and Prevotella spp. among others.

Results: In all participants we found the pH gradient in the lower reproductive canal to be most acidic in the lower vagina and most alkaline in the upper uterine cavity. Women with an abnormal vaginal microbiota had an increased pH in the lower vagina compared to the other groups.

Conclusions: There is a pronounced pH gradient within the female genital tract. This gradient is not disrupted in women with an abnormal vaginal microbiota.

Keywords: abnormal vaginal microbiota; bacterial vaginosis; cervical mucus plug; female reproductive tract; uterine pH; vaginal pH; vaginal physiology.

Figure 1

Technical illustrations of the calibration procedure (a) and measurement points (b) used for evaluating pH along the female genital tract. In (b) pH measuring points are market with a blue square, IN = introitus, MV = mid-vagina, FP = fornix posterior, DC = distal cervical canal, PC = proximal cervical canal, LU = lower uterine cavity, and UU = upper uterine cavity.

Figure 2

Box-and-whisker plots of the pH values measured along the genital tract in women at different stages of pregnancy (A) and in nonpregnant (B) and early-pregnant (C) women divided according to the identified vaginal microbiome. The horizontal line is plotted at the median; the box extends from the 25th to the 75th percentile; and the whiskers identify the maximum and minimum values. Data were compared by repeated measure two-way ANOVA followed by Sidak’s post hoc tests: * p < 0.05, ** p < 0.01, *** p < 0.001 vs. normal vaginal microbiota (NVM) or as indicated.