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INTRODUCTION AND HYPOTHESIS: We sought to determine age-related changes to the pelvic floor in the absence of childbirth effects. METHODS: A case-control study was conducted from June 2017–August 2018 comparing two groups of nulliparous women

INTRODUCTION AND HYPOTHESIS: This study aimed to: 1) measure levator ani bowl volume at rest and while straining, 2) compare women with and without prolapse (controls), and 3) assess the ability of measures of mid-sagittal bowl area, levator hiatus (LH), and urogenital hiatus (UGH) to predict bowl volume. METHODS: Forty MRI scans previously acquired in case-control prolapse studies including 20 women with prolapse and 20 women without prolapse, of similar age and parity, were selected. 3D models of rest and strain bowl volumes were made using sagittal scans and 3D Slicer®. Mid-sagittal bowl area, UGH, and LH were measured with ImageJ. Data were analyzed using two sample t-tests, effect sizes, and Pearson’s correlation coefficients at the 0.05 significance level. RESULTS: Data were acquired in a total of 40 total women. Levator bowl volume at strain had a correlation coefficient of 0.5 with bowl volume at rest. During straining, prolapse subjects had a 53% larger bowl volume than control subjects (254 ± 86 cm(3) vs. 166 ± 44 cm(3), p0.75). The strongest correlation with straining bowl volume was straining bowl area (r=0.86), followed by LH strain (r=0.80), then UGH strain (r=0.76). CONCLUSIONS: Straining levator bowl volume is substantially different than measures made at rest, with only a quarter of straining values explained by resting measurements. The bowl area at strain is the best 2D measurement estimating bowl volume and explains 74% of straining bowl volume.

Background Pelvic organ prolapse has 2 components: (1) protrusion of the pelvic organs beyond the hymen; and (2) descent of the levator ani. The Pelvic Organ Prolapse Quantification system measures the first component, however, there remains no standard measurement protocol for the second mechanism. Objective We sought to test the hypotheses that: (1) difference in the protrusion area is greater than the area created by levator descent in prolapse patients compared with controls; and (2) prolapse is more strongly associated with levator hiatus compared to urogenital hiatus. Study Design Midsagittal magnetic resonance imaging scans from 30 controls, 30 anterior predominant, and 30 posterior predominant prolapse patients were assessed. Levator area was defined as the area above the levator ani and below the sacrococcygeal inferior pubic point line. Protrusion area was defined as the protruding vaginal walls below the levator area. The levator hiatus and urogenital hiatus were measured. Bivariate analysis and multiple comparisons were performed. Bivariate logistic regression was performed to assess prolapse as a function of levator hiatus, urogenital hiatus, levator area, and protrusion. Pearson correlation coefficients were calculated. Results The levator area for the anterior (34.0 ± 6.5 cm 2 ) and posterior (35.7 ± 8.0 cm 2 ) prolapse groups were larger during Valsalva compared to controls (20.9 ± 7.8 cm 2 , P 2 ) and posterior (14.4 ± 5.7 cm 2 ) prolapse groups were both larger compared to controls (5.0 ± 1.8 cm 2 , P P P 2 vs 9.4 ± 5.9 cm 2 , P P ≤ .001, for all comparisons). Conclusion In prolapse, the levator area increases more than the protrusion area and both the urogenital hiatus and levator hiatus are larger. The odds of prolapse for an increase in the urogenital hiatus are 3 times larger than for the levator hiatus, which leads us to reject both the original hypotheses.