Objective To explore the clinical value of Z-score in evaluating the performance of pelvic diaphragmatic fissure expansion.MethodsA total of 202 women without pelvic organ prolapse（POP）were selected as the control group.The parameters of levator hiatus（anterior-posterior diameter

coronal diameter and area）obtained by three-dimensional ultrasound at rest were used as the independent variable and the parameters on Valsalva were used as the dependent variable for linear regression analysis.The performance parameters of pelvic diaphragmatic fissure expansion were determined and the Z-score model was established based on the results.The parameters of 259 women with POP（POP group）on Valsalva were imported into the Z-score model to evaluate the degree of expansion.The receiver operating characteristic（ROC）curve was used to test the statistical value of Z-score.ResultsThere was good correlation between the area of levator hiatus at rest and on Valsalva in the control group（r=0.74

P<0.05）.The Z-score model was established with the parameter of levator hiatus area:Z score=（actual observed value-17.37）/3.00.The Z-score value of the POP group was higher than that of the control group

and increased with the degree of POP.The difference between the two groups was statistically significant（P<0.05）.ROC curve analysis confirmed the value of Z-score had high sensitivity and specificity in diagnosing abnormal expansion of the pelvic diaphragmatic hiatus.For POP grade Ⅱ

When the Z-score value was 0.86

the sensitivity and the specificity were 0.90 and 0.80

respectively.For POP grade Ⅲ

When the Z-score value was 1.83

the sensitivity and specificity were 0.89 and 0.96

respectively.Conclusion Zscore can be used to evaluate the expansion of the pelvic diaphragm hiatus scientifically and quantitatively

when Z-score ≥0.86

it can be diagnosed as abnormal expansion of the pelvic diaphragm hiatus.