Female stress urinary incontinence (SUI) is closely linked to the weakening of pelvic floor muscles, often due to childbirth, aging, or hormonal changes. Pelvic floor muscle training (PFMT) is widely recognized as an effective treatment for lower urinary tract symptoms (LUTS), including SUI. However, some individuals are unable to perform PFMT effectively, reducing its benefits. On the other hand, the transversus abdominis (TVA) muscle, a key component of core stability, has been found to correlate strongly with pelvic floor muscle strength. Additionally, vaginal pressure (VP) serves as a useful indicator of pelvic floor function, reflecting the contractile force generated by these muscles.
While pelvic floor dysfunction is also implicated in the onset of overactive bladder (OAB), the specific relationships among OAB symptoms, VP, and TVA thickness remain unclear. In this study, we aimed to investigate the associations between OAB onset, VP, and TVA muscle thickness in women.

Participants included female LUTS patients newly diagnosed with OAB and women without OAB as controls. Patient characteristics, VP during maximal contraction, and TVA thickness were compared between the two groups. Participants were further categorized into three groups based on the Overactive Bladder Symptom Score (OABSS): non-OAB (0–2), mild OAB (3–5), and moderate/severe OAB (6–15). We statistically analyzed the relationships between OAB severity, VP, and TVA thickness.

A total of 106 patients were included in the OAB group and 107 in the non-OAB group. Patients in the OAB group were significantly older (P<0.001) and had a higher body mass index (BMI) (P<0.001) than those in the non-OAB group. VP during maximal contraction was significantly lower in the OAB group (18.0 ± 9.0 vs. 28.4 ± 12.3 cmH₂O, P<0.001), while the duration of contraction showed no significant difference (P=0.965).
TVA thickness was measured in the supine position at rest, maximal inspiration, maximal expiration, and maximal TVA contraction. At all points, TVA thickness was lower in the OAB group (P=0.014 at rest; P<0.001 at other points).
Significant differences in TVA thickness and VP were observed across OAB severity levels. Of the four measurement points, maximal TVA contraction showed the strongest association with OAB onset (r=0.330, P<0.001). Detailed study of the relationship between OAB morbidity and VP and TVA thickness at maximal TVA contraction revealed that the areas under the curve were 0.756 and 0.730, respectively; the cut-off for VP at OAB onset was 20.0 cmH2O (sensitivity 0.698, specificity 0.786, P<0.001) and the cut-off for TVA thickness was 4.45 mm (sensitivity 0.702, specificity 0.692, P<0.001).
Multivariate analysis identified low VP, reduced TVA thickness, high blood pressure, and high BMI as significant risk factors for OAB onset. The odds ratios (OR) were: VP, OR 3.53 (95% CI 1.14–6.39, P<0.001); TVA thickness, OR 2.84 (95% CI 1.37–6.01, P=0.005).

This study shows that women with OAB have lower VP and thinner TVA compared to those without OAB. Both measures decline with increasing OAB severity, especially TVA thickness during maximal contraction. These factors were significant predictors of OAB, and multivariate analysis identified low VP, reduced TVA thickness as independent risk factors. The results suggest that pelvic floor and core muscle weakness is linked not only to OAB onset but also to its severity.

This study suggests that reduced VP and decreased TVA thickness, particularly during maximal contraction, are associated with both the onset and severity of OAB in women. These findings highlight the potential role of pelvic floor and core muscle function in OAB assessment and prevention.