Levator-Urethra Gap: Normative Data in a Nonpregnant Nulliparous Population.

Objective: This study aimed to establish a normative range of the levator-urethra gap (LUG) measurement in nonpregnant, nulliparous women to be used as a standard against which assessments of injury or avulsion of the levator ani could be made.

Methods: Nulliparous women in the Pacific Northwest who were planning pregnancy within the ensuing 12 months underwent high-resolution magnetic resonance imaging (MRI) and 3-dimensional transperineal ultrasonography. In the plane of minimal hiatal dimensions, the LUG was measured on both the right and left sides for 3 contiguous image slices.

Results: One hundred thirty-five participants underwent examinations, of which 134 had evaluable MRIs and 70 had evaluable ultrasounds. Mean (SD) age was 30.8 (4.0) years, and mean (SD) body mass index was 25.9 (6.4). The majority of the participants self-identified as White (80%) and non-Hispanic (89%). The 99th percentile was no greater than 2.39 cm on any slice for either MRI or US-based measurements. In the MRI set, the lowest LUG values at which all 3 measurements on a side were found to have exceeded a putative threshold value (for injury) were 2.1 cm for the right side and 2.05 cm for the left side. The corresponding LUG values in the ultrasound set were 2.2 cm on the right and 2.25 cm on the left.

Conclusions: The LUG threshold in 3 successive slices in the minimal hiatal dimension suggestive of levator ani injury could be as low as 2.1 cm when using MRI and 2.25 cm when using ultrasound in a similar population.