Obstetric risk factors for stress urinary incontinence: a population-based study.

OBJECTIVE: To evaluate obstetric and maternal risk factors for stress urinary incontinence.
METHODS: We linked three national, Swedish, population-based registries with the use of unique personal identification numbers. All women born between 1932 and 1977 and operated on for stress urinary incontinence between 1987 and 1996 were identified from the Hospital Discharge Registry. This information was linked with the Medical Birth Registry (for the years 1973-1995), containing information on antenatal care, delivery, and the newborn, and the Fertility Registry (for the years 1932-1997), containing information on the number of children delivered by each Swedish woman. For determination of odds ratios (ORs) and approximate 95% confidence intervals (CIs), we used the Mantel-Haenszel method and a test-based method after suitable stratifications and exclusions.
RESULTS: Diabetes mellitus, body mass index (BMI), age at first delivery, parity, birth weight, and epidural analgesia were positively associated with incontinence surgery. In contrast, cesarean delivery, forceps/vacuum extraction, and episiotomy were negatively associated with incontinence surgery. No association was found between surgery for stress incontinence and age at last delivery, smoking during pregnancy, level of education, multiple birth, large perineal tear, or breech presentation at any vaginal delivery. The OR for incontinence surgery was similarly decreased for nulliparous women and for uniparous women delivered by elective cesarean.
CONCLUSION: Vaginal delivery, notably the first, is strongly associated with later surgery for stress incontinence, but the association is modified by maternal conditions and interventions during delivery. No association was found between surgery for stress incontinence and pregnancy per se.