Racial differences in the structure and function of the stress urinary continence mechanism

Objective: To compare the structure and function of the urethral sphincter and the urethral support in nulliparous black and white women. Methods: Eighteen black women (mean age 28.1 years) and 17 white women (mea n age 31.3 pears) completed this cross-sectional study. The following asses sments were made: urethral function using multichannel cystometrics and ure thral pressure profilometry, pelvic muscle strength using an instrumented s peculum, urethral mobility using the cotton-swab test and perineal ultrasou nd, and pelvic muscle hulk using magnetic resonance imaging. Results: Black women demonstrated a 29% higher average urethral closure pre ssure during a maximum pelvic muscle contraction (154 cm H2O versus 119 cm H2O in the white subjects; P = .008). Although not statistically significan t, black women had a 14% higher maximum urethral closure pressure at rest ( 108 cm H2O versus 95 cm H2O; P = .23) and a 21% larger urethral volume (481 8 mm(3) versus 3977 mm(3); P = .06). In addition, there was a 36% greater v esical neck mobility measured with the cotton-swab test (blacks 49 degrees versus whites 36 degrees; P = .02) and a 42% difference in ultrasonically m easured vesical neck mobility during a maximum Valsalva effort (blacks = -1 7 mm versus whites -12 mm; P = .08). Conclusion: Functional and morphologic differences exist in the urethral sp hincteric and support system of nulliparous black and white women. (C) 2000 by The American College of Obstetricians and Gynecologists.