Using Z ‐scores to evaluate levator hiatal dimensions with four‐dimensional translabial ultrasound

Aim This study represents the first attempt to use ‘ Z ‐scores’ to assess levator hiatal dimensions and quantify hiatal expansion. Methods We undertook a retrospective study on the data of 110 nulliparae and 73 pelvic organ prolapse (POP) patients who had a clinical POP exam and translabial 4‐D ultrasound. We used Z ‐scores to normalize the dimensions of nulliparae levator hiatus and to build a Z ‐score model to evaluate the ‘hiatal ballooning’ against the POP staging. Results Valid data were gathered from 102 nulliparae and 64 POP patients. We built the Z ‐score models as follows: Z ‐Av = (measured value – 17.19) / 2.98, Z ‐Lv = (measured value – 55.65) / 5.48, where ‘Av’ and ‘Lv’ represented the ‘hiatal area’ and the ‘anterior–posterior diameter’ on Valsalva, respectively. The ‘90% reference range’ of Z ‐Av was (−1.8−+1.8) and that of Z ‐Lv was (−2.0−+2.0). On receiver–operator curve analysis, the cut‐off against POP stage 2 for Av was 20 cm 2 (sensitivity of 79%, specificity of 66%), and that for Lv was 6.0 cm (sensitivity of 68%, specificity of 65%), which were approximately equal to a Z ‐Av of 1.0 and a Z ‐Lv of 1.0, correspondingly. For POP stage 3, the cut‐off was an Av of 24 cm 2 (sensitivity of 85%, specificity of 83%) or an anterior–posterior diameter of 6.3 cm (sensitivity of 77%, specificity of 80%), which was approximately equal to a Z ‐Av of 2.0 or a Z ‐Lv of 1.5, respectively. Conclusion ‘Normal hiatal dimension’ was defined as Z ‐Av ≤ 1.0 or Z ‐Lv ≤ 1.0, and ‘hiatal ballooning’ was defined as Z ‐Av ≥ 2.0 or Z ‐Lv ≥ 1.5.