Three-dimensional pelvic floor ultrasound measuring levator ani hiatus area and its association with pelvic organ prolapse: a population based retrospective cross-sectional study in Chinese women

Background The levator ani hiatus (LAH) area is closely associated with the occurrence and severity of pelvic organ prolapse (POP). However, no current data on the definition of normal hiatal dimensions in Chinese women have been published. This study aimed to assess the cut-off area of the LAH for the occurrence of objective and severe POP in Chinese women based on a retrospective cross-sectional study with a large sample. Methods Women from the Postpartum Clinic and Rehabilitation Center of the Pelvic Diseases and Urogynecologic Department of a tertiary hospital were recruited between May 2017 and November 2022. All women underwent Pelvic Organ Prolapse Quantification grading and three-dimensional pelvic floor ultrasonography examinations performed by experienced doctors. The LAH area was measured at resting and maximum Valsalva states using ultrasonography. The association between the hiatal areas and the stages of prolapse was analyzed using the univariant Chi-squared test and Wilcoxon rank sum test. Receiver operating characteristic curve analysis was used to obtain the cut-off area of the LAH for the occurrence of objective and severe POP. Results Overall, 1,633 women were recruited in this study. The hiatal area at rest showed a significant association with POP severity, especially in stages 1, 2, and 3. Larger hiatal areas at rest were correlated with more advanced prolapse stages. For the anterior vaginal wall, a cut-off hiatal area of 14.45 cm2 at rest yielded a sensitivity of 0.57 and a specificity of 0.65 [area under the curve (AUC): 0.65; 95% confidence interval (CI): 0.62–0.68] for significant objective POP, which was the smallest among the three pelvic zones. In cases involving the uterus or vaginal fornix, a cut-off hiatal area of 20.30 cm2 at rest achieved a sensitivity of 0.39 and a specificity of 0.75 (AUC: 0.57; 95% CI: 0.50–0.64) for severe POP, representing the largest cut-off among the three pelvic zones. Conclusions For Chinese women, we suggest a cut-off of 14.45 cm2 at rest for ‘normal’ LAH and the hiatal area of ≥20.30 cm2 at rest for a close correlation with severe POP.