Evaluating Z Scores to Quantify Levator Hiatal Distensibility by 3-Dimensional Ultrasonography in Nulliparas and Women With Pelvic Organ Prolapse.

Hiatal distensibility can be exactly evaluated by Z-Av. A Z-Av value of less than 1.0 was defined as a "normal hiatal expansion," 1 to 3 as "mild ballooning," 3 to 5 as "moderate ballooning," 5 to 7 as "marked ballooning," and 7 or greater as "severe ballooning."