Vaginal birth and de novo stress incontinence: relative contributions of urethral dysfunction and mobility.

OBJECTIVE: To evaluate the relative contributions of urethral mobility and urethral function to stress incontinence. METHODS: This was a case-control study with group matching. Eighty primiparous women with self-reported new stress incontinence 9-12 months postpartum were compared with 80 primiparous continent controls to identify impairments specific to stress incontinence. Eighty nulliparous continent controls were evaluated as a comparison group to allow us to determine birth-related changes not associated with stress incontinence. Urethral function was measured with urethral profilometry, and vesical neck mobility was assessed with ultrasound and cotton swab test. Urethral sphincter anatomy and mobility were evaluated using magnetic resonance imaging. The associations among urethral closure pressure, vesical neck movement, and incontinence were explored using logistic regression. RESULTS: Urethral closure pressure (+/-standard deviation) in primiparous incontinent women (62.9+/-25.2 cm H(2)0) was lower than in primiparous continent women (83.9+/-21.0, P<.001; effect size d=0.91) who were similar to nulliparous women (90.3+/-25.0, P=.091). Vesical neck movement measured during cough with ultrasonography was the mobility measure most associated with stress incontinence; 15.6+/-6.2 mm in incontinent women compared with 10.9+/-6.2 in primiparous continent women (P<.001, d=0.76) or nulliparas (9.9+/-5.0, P=.322). Logistic regression disclosed the two-variable model (max-rescaled R(2)=0.37, P<.001) was more strongly associated with stress incontinence than either single-variable model, urethral closure pressure (R(2)=0.25, P<.001) or vesical neck movement (R(2)=0.16 P<.001). CONCLUSION: Lower maximal urethral closure pressure is the measure most associated with de novo stress incontinence after first vaginal birth followed by vesical neck mobility. LEVEL OF EVIDENCE: II.