The association between the vaginal microenvironment and fecundability: a register-based cohort study among Chinese women
The vaginal microenvironment hosts a range of bacteria and other elements, such as inflammatory cells and metabolites, at an optimal pH level. In this ecosystem, sexually transmitted infections, such as chlamydia and gonorrhoea, are well known causes of female infertility.
Recent studies utilising next generation sequencing (NGS) technology suggest a possible link between abnormal vaginal microbiota composition and cases of idiopathic infertility, with reduced pregnancy rates following IVF treatment.
These studies however only investigated the microenvironment of infertile women, and not the general population, therefore the broader effect of the vaginal microenvironment on fecundability is currently unknown.
To explore the association between the vaginal microenvironment and female fecundability using the Amsel criteria and vaginal cleanliness grade system.
The National Free Pre-conception Check-up (NFPCP) registry database in China was analysed for this study.
The study cohort included women aged 20 to 49 years, not pregnant during check-up, with male partners aged > 22 years and planning to conceive.
Any woman or partner diagnosed with infertility or malformation of the reproductive system, requiring fertility treatment or positive for infection, was automatically excluded from the study, along with any woman who failed to test for infections or did not confirm their fertility status one year after check-up.
Demographic characteristics was captured using a standardised questionnaire followed by face-to-face interviews to collect blood samples, measure BMI, establish blood pressure, menstrual status, tobacco use and alcohol intake.
Vaginal swabs were also collected from each woman, by a gynaecologist, to carry out a pH test, clue cell evaluation, whiff test and vaginal cleanliness grading.
A pH < 4.5 was defined as normal, while clue cell tests were positive if > 20% clue cells was visible after covering vaginal epithelial cells with non-Lactobacilli bacteria on a wet mount slide. For the whiff test, a fishy amine smell after adding 10% potassium hydroxide to the vaginal fluid solution was deemed positive. Vaginal cleanliness was assessed based on the distribution of Lactobacillus and other flora, epithelial cells, and white blood cells under a basic microscopy, with grades I and II considered normal, and III and IV deemed poor.
Overall a normal vaginal microenvironment was defined by a pH < 4.5, < 20% of clue cells visible on wet mount, negative whiff test, and a vaginal cleanliness grade ≤ II.
Main study outcome was clinical pregnancy, confirmed by hospital pelvic ultrasound scan. Women who achieved pregnancy within the one-year follow-up period were classified as fertile, while women who did not, were regarded as sub-fertile.
In total 3,388,554 women satisfied the inclusion exclusion criteria, of which 379,718 (11.2%) had a poor vaginal microenvironment.
Interestingly the mean age between the poor and normal groups was significantly higher (28.8 vs. 22.8 years). This translated into significant differences, regarding baseline characteristics, between the 2 groups. To eliminate these baseline differences and confounders, propensity score matching (PSM) was used to match each participant with a poor sample to a similar participant with a normal sample.
In this matched dataset, women with a poor vaginal microenvironment had a statistically significant reduction in the overall pregnancy rates (71.8 vs. 73.5 %, P<0.001), translating into a 9% decrease in the probability of getting pregnant (FOR=0.91).
Population attributable risk percentage (PARP) analysis indicated that subfertility in 10.8% of women could be attributed to a poor vaginal microenvironment.
Sub-analysis of the results according to each microenvironment test showed that vaginal cleanliness, had the greatest effect on fecundability, with grade III and IV, causing a 14% and 23% reduction in the probability of being pregnant after 1 year respectively. Women who tested positive on the clue cell test demonstrated a 12% reduction in fecundability, while a positive whiff test was associated with a 7% reduction in the probability of being pregnant after 1 year. Interestingly a pH ≥ 4.5 was the least concerning with only a 1% reduction in fecundability calculated.
Unsurprisingly women with irregular menstrual cycles and poor vaginal microenvironments demonstrated a further reduction on fecundability (-14%) compared to women with normal cycles (-8%).
This was also significantly different between multipara (-11%) and nulliparous women (-2%) for unknown reasons.
The authors noted that recommended lifestyle choices, such as healthy diet, exercise, vulva cleaning (douching) with water and good perineal hygiene effect on fecundability, remains to be proven.
SUMMARY: CAN DOUCHING PREVENT PREGNANCY
In this study, women with poor vaginal cleanliness, had the lowest probability of falling pregnant, with a reduction in fecundability of 14% and 23%, associated with cleanliness grades III and IV respectively, highlighting a potential role for douching in maintaining an optimal microenvironment.
- Only one sample collected per woman.
- Vaginal microbiota and enzymes not assesed by RNA or NGS methods.
- Chinese only population study.
This research was supported by grants from the National Key Research and Development Program of China, National Natural Science Foundation of China, CAMS Innovation Fund for Medical Sciences, National Human Genetic Resources Sharing Service Platform and National Population and Reproductive Health Science Data Center.
A distortion that modifies the estimated measure of an association.
Variables, i.e. participant characteristics, that may affect the result.
Cells on the surface of the body that form a protective barrier.
The probability of conception in a single menstrual cycle.
Fecundability Odds Ratio.
Community of micro-organisms.
A woman that has had more than one pregnancy resulting in a live birth.
A woman that has never given birth.
Hong x, et al. (2020). The association between vaginal microbiota and female infertility: a systematic review and meta-analysis. https://doi.org/10.1007/s00404-020-05675-3
Campisciano G, et al. (2017). Subclinical alteration of the cervical-vaginal microbiome in women with idiopathic infertility. https://doi.org/10.1002/jcp.25806
Haahr H, et al. (2016). Abnormal vaginal microbiota may be associated with poor reproductive outcomes: a prospective study in IVF patients. https://doi.org/10.1093/humrep/dew026
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