Vaginal Birth and Stress Urinary Incontinence

Damages to the muscles and fasciae of the female pelvic floor that occur during vaginal delivery are the most important known causes of stress urinary incontinence (SUI) in women. This study tries to explain the relation between damage of both, 1) the urethral support system, and 2) the sphincteric control system and the occurrence of SUI by means of modern imaging and methods of clinical pressure - and force measurement. Hypothesis: Vaginal delivery causes SUI through a combination of damages to the urethral support and the sphincter control system. Study design: Case control design; Cases are primiparous women with stress incontinence (SI; n=80) persisting 6 months postpartum, negative controls are nulliparous continent women (NC; n=80), and positive controls are primiparous continent women (PC; n=80) after vaginal delivery. We will quantify urethral support and sphincteric function in each of these groups using magnetic resonance imaging and ultrasonography of the pelvic floor, levator strength measurements and urethral pressure studies. Primary hypotheses: 1) Measurements of either urethral support or sphincteric control system alone will predict less than 30% of SI cases. 2) Identify the combinations of support and sphincter parameters, which have at least an 80% probability of correct prediction of SI compared with PC or NC. 3) Identify the relative importance of support parameters, sphincter parameters, and their interactions by construction of a predictive model for SUI using discriminant functions and classification trees. Secondary hypotheses: 1) Loss of urethral support involves connective tissue breaks and/or loss of levator ani bulk measurable on MRI. 2) Sphincteric weakness results from quantifiable loss of sphincter bulk. Other aims: 1) Construct and validate a computer model of the mechanisms of injury responsible for sphincter and support damage occurring during vaginal delivery. 2) Establish the priority of obstetrical parameters associated with SUI. The importance of this research lies in the insights about the specific functional and anatomical defects caused by vaginal delivery. These insights will help in devising future injury prevention at birth and will help to form the basis for treatment selection in women with stress urinary incontinence.