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

BACKGROUND: Vaginal birth increases the chance a woman will develop stress incontinence. This study evaluates the relative contributions of urethral mobility and urethral function to stress incontinence. METHODS: This is a case-control study with group matching. Eighty primiparous women with self-reported new stress incontinence 9–12 months postpartum were compared to 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 Q-tip test. Urethral sphincter anatomy and mobility were evaluated using MRI. The association between urethral closure pressure, vesical neck movement, and incontinence were explored using logistic regression. RESULTS: Urethral closure pressure in primiparous incontinent women (62.9 +/− 25.2 s.d. cm H(2)0) was lower than in primiparous continent women (83.0 +/− 21.0, p<0.001; effect size d= 0.91) who were similar to nulliparous women (90.3 +/− 25.0, p=0.09). Vesical neck movement measured during cough with ultrasound was the mobility parameter most associated with stress incontinence; 15.6 +/− 6.2 mm in incontinent women versus 10.9 +/− 6.2 in primiparous continent women (p < 0.0001, d = 0.75) or nulliparas (9.9 +/− 5.0, p=0.33). Logistic regression disclosed the two-variable model (max-rescaled R(2) =0.37, p < 0.0001) was more strongly associated with stress incontinence than either single variable models, urethral closure pressure (R(2) = 0.25, p <0.0001) or vesical neck movement (R(2) = 0.16 p < 0.0001). CONCLUSIONS: Lower maximal urethral closure pressure is the parameter most associated with de novo stress incontinence after first vaginal birth followed by vesical neck mobility