Anatomical Differences in Levels of Support Between Chinese and Caucasian Women

Objectives: Pelvic floor anatomy including level I, II and III has clinical implications. Our objective was to quantify the differences in pelvic floor support among Chinese and Caucasian nulliparous women.

Methods: This was a retrospective cross-sectional study of a convenience sample of Chinese and Caucasian identifying nulliparous women with normal pelvic floor support (no prolapse at/below the hymen). All subjects underwent similar pelvic floor 3D MRIs at rest. MRIs were analyzed (Image J, 3D slicer v. 4.11) and measurements included 1) Level I support: cardinal ligament curve length and angle, sacrum-apex distance and angle, and apex location; 2) Level II support: anterior vaginal length and vaginal width at the level of anterior fornix, mid-vagina, and urethra-vaginal junction (UVJ); 3) Level III support: urogenital hiatus (UGH) anterior-posterior (AP) diameter, levator hiatus (LH) AP diameter, levator area (highlighted with blue shade in figure 1A) and perineal body (PB) location; 4) bony pelvis dimensions: ischial spine distance, sacrococcygeal-inferior pubic point (SCIPP) length and angle (Figure 1). Apex and PB location were measured relative to the Pelvic Inclination Correction System (PICS) line, 34° below the SCIPP line. Bivariate comparisons with standard t-tests were used for analysis. Multiple comparisons were adjusted using Bonferroni correction: p-values less than 0.05 divided by 16 comparisons (p < 0.003) were considered as statistically significant. Effect size (Cohen’s d) of the differences were also reported.

Results: The study sample included 31 Chinese and 31 Caucasian women with similar age (24.8 vs 25.0 years; p=.87), BMI (22.7 vs 23.9 kg/m2; p=.18), and height (163 vs.164 cm; p=.41). In Chinese women, the apex was found to be 19% lower (44 vs 54 mm; p < .001) and the cardinal ligament length was 20% longer (71 vs 59 mm; p=.001). The anterior vaginal length was 12% shorter in Chinese nulliparas (54 vs 61 mm; p < .001) and 14% narrower at the mid-level of vagina (33 vs 38 mm; p=.002). UGH AP diameter was 14% smaller (24 vs 28 mm; p=.002), and the PB location was 38% higher (-8 vs -13 mm; p=.003) in Chinese women. For bony dimensions, Chinese women had a a 5% wider ischial spine distance (111 vs 105 mm; p=.005). Figure 2 demonstrates the groups’ difference graphically and effect sizes of the group differences. Height adjusted calculations showed no significant differences in the above results.

Conclusions: Despite similar heights and BMI, we found differences in all three levels with the largest difference in Level I, followed by Level II, Level III, and lastly bony dimensions. Comment: These differences in pelvic floor anatomy between Chinese and Caucasian women may influence the risk of birth injury, prevalence and mechanism of prolapse, treatment outcomes, and product design.