Introduction

Vaginal Relaxation Syndrome (VRS), a type of pelvic floor dysfunction, is a common postpartum issue in women, with an incidence rate of up to 20%. VRS compromises the structural integrity of the vaginal wall and disrupts the vaginal microbiota, resulting in reduced self-cleaning ability. This condition increases the risk of pathogenic overgrowth and recurrent infections, including bacterial vaginitis. The diminished self-cleansing function of the vagina makes it more susceptible to pathogenic invasion, significantly raising the risk of recurrent vaginitis in affected patients1. Recurrent vaginitis not only causes physical discomfort but may also negatively impact patients’ psychological well-being. Currently, various treatment methods are available for VRS in clinical practice. Among these, fractional CO2 laser therapy, as a novel treatment modality, has shown promising results in alleviating VRS symptoms2. Studies have demonstrated that fractional CO2 laser therapy not only improves the symptoms of VRS but also potentially enhances the vaginal microecology by repairing the structure and function of vaginal wall tissues and cells. These improvements include increasing lactobacilli abundance and lowering vaginal pH levels3. Although fractional CO2 laser therapy has shown potential in VRS treatment, there is a lack of in-depth research on whether it can significantly enhance the efficacy and safety of treating recurrent bacterial vaginitis by improving the vaginal microecology in VRS patients.

This study aims to thoroughly investigate the efficacy of fractional CO2 laser therapy in treating patients with VRS combined with recurrent bacterial vaginitis, with a particular focus on its role in improving vaginal microecology and the correlation between these improvements and the restoration of vaginal function. Through this research, we hope to provide new insights and evidence for the clinical treatment of VRS combined with recurrent bacterial vaginitis, as well as theoretical support for the broader application.

Materials and methods

The study was approved by the Medical Ethics Committee of Guilin People’s Hospital (Approval Number: 2021-024KY) and conducted in accordance with ethical standards. All patients sign informed consent forms.

Study subjects

The study enrolled VRS patients with recurrent bacterial vaginitis who attended the gynecology outpatient clinic at Guilin People’s Hospital between July 2021 and December 2023. Inclusion Criteria: (1) VRS, characterized by a vaginal diameter that can accommodate two or more fingers(Diagnostic criteria: Supplementary material s1), combined with recurrent bacterial vaginitis (three or more episodes per year), is diagnosed based on increased vaginal discharge, using the Amsel criteria, thin and homogeneous consistency, foul odor, vaginal pH > 4.5, positive amine test, and > 20% clue cells under microscopic examination. A diagnosis requires three of these criteria, with the fourth being the gold standard; (2) There are no contraindications for the use of fractional CO2 laser or electrotherapy; (3) Women aged 20 to 45 years History of at least one vaginal delivery; (4) Vaginal diameter ranging from greater than 2 fingers to 4 fingers, assessed by the same senior attending physician, with no presence of uterine prolapse, vaginal tumors, or other complications. Exclusion criteria: (1) Pregnant or lactating women; (2) Patients with sexually transmitted infections; (3) Patients with severe cardiovascular, metabolic, neurological diseases, or mental disorders; (4) Acute inflammatory genital infections; (5) History of laser allergy or photosensitivity; (6) Previous vaginal tightening surgery. A total of 120 patients were included in the study, with odd-numbered patient IDs assigned to the intervention group (n = 60) and even-numbered patient IDs assigned to the control group (n = 60).

Methods

Treatment methods

The control group received oral metronidazole at a dosage of 0.4 g per dose, administered twice daily for 7 days. The observation group received fractional CO2 laser therapy in addition to the control group’s treatment. The laser device used was the SmartXide2 C60, manufactured by DEKA Laser Company, Italy. Following routine disinfection of the vulva and vagina, lidocaine cream was applied locally, and the 360° CO2 laser probe was used for intravaginal treatment. The parameters were as follows: emission mode DP (DEPA pulse), energy 30–40 J/s, exposure time 800–1000 ms, and spot spacing 800–1000 μm. Single or double excitation was applied. The procedure involved positioning the probe at the vaginal apex, emitting the laser to scan the vaginal area 360°, and retracting the probe uniformly to avoid gaps. Patients received three treatments, with each session spaced 28 to 42 days apart. Sexual intercourse was prohibited for 2 weeks following each treatment.

Evaluation criteria

Vaginal pH testing

The vaginitis combined detection kit (enzyme chemical reaction method) from Shenzhen Ruitu Biotechnology Co., Ltd. was used for detection.

Semi-quantitative detection of vaginal lactobacilli

Vaginal secretions were prepared into smears of uniform thickness, stained, and examined under the oil immersion lens. The arrangement and distribution of bacteria were observed, and the average content of Lactobacillus was recorded by counting in 10 fields. The evaluation criteria for Lactobacillus content were based on the Expert Consensus on Clinical Application of Vaginal Microecological Evaluation4.

Vaginal laxity grading5

A vaginal diameter accommodating 2–3 fingers indicates mild laxity, characterized by slight vaginal enlargement and reduced sensation during intercourse. A diameter accommodating 3–4 fingers indicates moderate laxity, associated with symptoms such as vaginal dryness, dyspareunia, yellow or brown spots on pads or underwear, frequent urination, and urinary incontinence. A diameter accommodating more than 4 fingers indicates severe laxity, with symptoms including vaginal prolapse, eversion, constipation, and incomplete bowel movements.

Vaginal health index (VHI)

The Vaginal Health Index (VHI) evaluates the vaginal mucosal environment, including vaginal moisture, secretion type and consistency, epithelial morphology, and mucosal elasticity, with scores ranging from 1 to 5. Higher scores reflect better mucosal conditions6.

Statistical methods

Statistical analysis was conducted using SPSS version 25.0. Normally distributed quantitative data were expressed as mean ± standard deviation (x̄ ± s), while categorical data were presented as counts (percentages). Comparisons between groups for normally distributed quantitative data were performed using t-tests, and categorical data were analyzed with chi-square tests or Fisher’s exact test. Correlation analysis was carried out using Spearman’s rank correlation. A p-value of less than 0.05 was considered statistically significant.

Results

Comparison of baseline indicators

Prior to treatment, there were no significant differences between the two groups in terms of age, body mass index (BMI), vaginal lactobacilli distribution, vaginal pH, or degree of vaginal laxity, confirming that the groups were comparable (P > 0.05). Refer to Tables 1, 2, 3, 4 and 5.

Table 1 Comparison of baseline indicators between the two groups before treatment [(\(\bar{\text{x}}\) ± s) / n(%)].
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Comparison of vaginal laxity

Post-treatment, the control group exhibited no significant improvement in vaginal laxity (χ2 = 0.371, P = 0.831). In contrast, the observation group demonstrated significant improvement in vaginal laxity (χ2 = 26.882, P = 0.000), which was superior to the control group’s improvement (χ2 = 25.553, P = 0.000), indicating statistical significance. Refer to Table 2.

Table 2 Comparison of vaginal laxity severity between two groups of patients before and after treatment [n(%)].
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Comparison of VHI scores

Post-treatment, both VHI scores and total scores significantly increased compared to pre-treatment scores (P < 0.05). Additionally, the observation group exhibited significantly higher VHI and total scores than the control group post-treatment (P = 0.000). Refer to Table 3.

Table 3 Comparison of VHI scores between two groups of patients before and after treatment (\(\bar{\text{x}}\) ± s).
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Comparison of vaginal lactobacilli distribution

Post-treatment, both groups exhibited significant improvements in vaginal lactobacilli distribution (P < 0.05). However, the observation group demonstrated a significantly greater improvement compared to the control group (P = 0.000). Refer to Table 4.

Table 4 Comparison of lactobacillus distribution before and after treatment in two patient groups [n(%)].
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Comparison of vaginal pH

Post-treatment, vaginal pH did not show a significant change in the control group (P = 0.218). In contrast, the observation group demonstrated a significant decrease in vaginal pH compared to both pre-treatment values and the control group (t = 2.854, P = 0.005; t = 3.398, P = 0.001). Refer to Table 5.

Table 5 Comparison of vaginal pH before and after treatment [(x ± s) / n(%)].
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Comparison of post-treatment recurrence rates

Three months after treatment, the recurrence rate in the intervention group was significantly lower than in the control group (6 cases [8.33%] vs. 22 cases [36.67%], χ2 = 27.844, P < 0.001).

Correlation analysis between vaginal lactobacilli distribution and VHI scores

After treatment, a strong positive correlation was observed between vaginal lactobacilli distribution and total VHI scores in the intervention group (R = 0.79), which was statistically significant (P < 0.001), as shown in Fig. 1.

Fig. 1
figure 1

Correlation between vaginal lactobacilli distribution and total VHI scores in the intervention group post-treatment.

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Discussion

Vaginal Relaxation Syndrome (VRS) is characterized by vaginal canal enlargement and decreased contractility. Histologically, VRS damages vaginal wall tissues and cells, impairing their structural and functional integrity7. The vagina, exposed to external environments, is susceptible to various pathogens, which can cause infections in both the vagina and other reproductive tract areas. Normal vaginal immune function depends on the integrity of its tissues and cells, which maintain an acidic environment dominated by lactobacilli to protect against pathogens8,9. Consequently, patients with VRS are prone to vaginal inflammation. While treatments can alleviate symptoms, they do not prevent recurrent infections by vaginal pathogens, leading to a high recurrence rate of vaginitis. Clinically, I often observe frequent vaginitis recurrences in VRS patients, causing significant distress and negatively affecting their physical and mental health and quality of life. Effective treatment of vaginal inflammation requires not only symptom and pathogen elimination but also restoration of the vaginal microecological balance.

In recent years, fractional CO2 laser therapy has become an effective treatment for Vaginal Relaxation Syndrome (VRS), demonstrating high efficacy and safety with no observed damage to surrounding tissues post-treatment10. Clinically, VRS patients receiving this therapy show fewer recurrences of vaginal inflammation. Evidence also suggests that fractional CO2 laser therapy enhances the local vaginal microecology. I hypothesize that this therapy improves the function of vaginal wall tissues and cells, thereby enhancing the vaginal microecological environment. This may aid in treating VRS with bacterial vaginitis and prevent recurrence. This study aims to investigate this hypothesis.

The study results lead to the following conclusions:

(1) Vaginal Laxity: Post-treatment, the control group did not show significant improvement in vaginal laxity compared to pre-treatment levels. In contrast, the intervention group demonstrated a significant reduction in vaginal laxity and performed better than the control group. These findings suggest that conventional drug treatment alone is ineffective in improving vaginal laxity in VRS patients.

(2) VHI Scores: The Vaginal Health Index (VHI), an objective measure of vaginal health, showed higher scores for both groups post-treatment compared to pre-treatment. Notably, the intervention group had significantly higher VHI and total scores than the control group post-treatment. These results indicate that while conventional drug therapy improves vaginal health, combining it with fractional CO2 laser treatment is more effective.

(3) Distribution of Vaginal Lactobacilli: Post-treatment, both groups showed improved distribution of vaginal lactobacilli compared to pre-treatment. However, the intervention group exhibited a significantly greater improvement than the control group. This indicates that while conventional drug therapy can enhance vaginal lactobacilli distribution, the addition of fractional CO2 laser treatment further amplifies this effect. This finding is consistent with international studies showing that fractional CO2 laser treatment improves vaginal microbiota, increasing lactobacilli from 30% pre-treatment to 79% post-treatment and significantly lowering vaginal pH levels3. The benefits of fractional CO2 laser treatment likely result from its ability to repair vaginal wall tissues at the cellular level through non-invasive superficial ablation and thermal stimulation, which promotes collagen fiber proliferation and remodeling without damaging surrounding tissues11. This process enhances collagen production, thickens the vaginal wall, and restores mucosal elasticity and hydration. Additionally, the therapy can restore the thickness of the vaginal mucosal squamous epithelium, rebuild a robust stratified squamous epithelium, increase glycogen storage in epithelial cells, and stimulate fibroblasts to synthesize new collagen and form new papillae12. These morphological changes support the use of fractional CO2 laser treatment for repairing vaginal mucosa and improving vaginal microecology.

(4) Vaginal pH: Post-treatment, there was no significant difference in vaginal pH levels in the control group compared to pre-treatment values. However, the intervention group exhibited significantly lower vaginal pH levels post-treatment compared to both pre-treatment levels and the control group. This suggests that while conventional drug therapy can enhance the distribution of vaginal lactobacilli, it does not significantly improve vaginal pH. This may be because the improvement in lactobacilli distribution in the control group (P = 0.46) is insufficient to affect the pH. In contrast, the substantial improvement in lactobacilli distribution in the intervention group resulted in a corresponding improvement in vaginal pH.

(5) Recurrence Rates: Three months after treatment, the recurrence rate in the intervention group was significantly lower compared to the control group. This indicates that fractional CO2 laser treatment, combined with conventional drug therapy, more effectively reduces the recurrence of VRS with bacterial vaginitis.

(6) Fig. 1 demonstrates a significant strong positive correlation between vaginal lactobacilli distribution and VHI scores in the treatment group after intervention (R = 0.79, P = 0.000), which suggests that the improvement in lactobacilli distribution is not only a key indicator of vaginal microecological restoration but may also directly contribute to the enhancement of vaginal health index (VHI) scores. Lactobacilli play a crucial role in maintaining vaginal health by sustaining an acidic environment (lowering pH levels) and inhibiting the growth of pathogens. Furthermore, fractional CO2 laser treatment may enhance the colonization and proliferation of lactobacilli by promoting collagen fiber remodeling and epithelial regeneration, thereby creating a more favorable microenvironment. This finding is consistent with the results of Athanasiou et al., who reported a significant increase in lactobacilli proportions; however, this study further quantified the correlation between lactobacilli distribution and VHI scores, providing new reference data for clinical evaluation. These results suggest that, in future clinical practice, monitoring lactobacilli distribution and VHI scores could be an effective approach to assess treatment outcomes and optimize therapeutic strategies, ultimately reducing recurrence rates and improving patients’ quality of life.

Limitations

This study has several limitations that should be considered when interpreting the results. Firstly, it was a single-center study, which may introduce variability in patient care and outcomes. Additionally, the relatively small sample size may limit the generalizability of our findings. Another important limitation is the absence of objective indicators, such as vaginal flora distribution and muscle strength tests, which could better reflect changes in vaginal function and microecology. Furthermore, while our study focuses on the efficacy of CO2 laser treatment for Vaginal Relaxation Syndrome (VRS) complicated by recurrent bacterial vaginosis, it did not explore the impact of laser treatment on other types of vaginal infections, including candidal infections, which are common in clinical practice. This omission represents a gap in understanding the broader potential of CO2 laser therapy. While the current study demonstrates promising results for improving VRS and reducing the recurrence of bacterial vaginosis, it is important to note that CO2 laser therapy is not intended as a first-line treatment for vaginitis. Future studies should explore the broader application of CO2 laser therapy in gynecological contexts, including its potential role in treating other forms of vaginal infections, to further validate its clinical efficacy and improve patient outcomes.

Conclusions

Combining fractional CO2 laser treatment with conventional drug therapy can more effectively improve Vaginal Relaxation Syndrome (VRS) complicated by recurrent bacterial vaginosis. This approach not only reduces the recurrence rate but may also achieve therapeutic effects by enhancing vaginal microecology.