OBJECTIVES: Current concepts based on referral center data suggest that pelvic floor injury from obstetric trauma is a major risk factor for fecal incontinence (FI) in women. In contrast, a majority of community women only develop FI decades after vaginal delivery, and obstetric events are not independent risk factors for FI. However, obstetric events are imperfect surrogates for anal and pelvic floor injury, which is often clinically occult. Hence, the objectives of this study were to evaluate the relationship between prior obstetric events, pelvic floor injury, and FI among community women. METHODS: In this nested case-control study of 68 women with FI (cases; mean age 57 years) and 68 age-matched controls from a population-based cohort in Olmsted County, MN, pelvic floor anatomy and motion during voluntary contraction and defecation were assessed by magnetic resonance imaging. Obstetric events and bowel habits were recorded. RESULTS: By multivariable analysis, internal sphincter injury (cases - 28%, controls - 6%; odds ratio (OR): 8.8; 95% confidence interval (CI): 2.3-34) and reduced perineal descent during defecation (cases - 2.6±0.2 cm, controls - 3.1±0.2 cm; OR: 1.7; 95% CI: 1.2-2.4) increased FI risk, but external sphincter injury (cases - 25%, controls - 4%; P<0.005) was not independently predictive. Puborectalis injury was associated (P<0.05) with impaired anorectal motion during squeeze, but was not independently associated with FI. Grades 3-4 episiotomy (OR: 3.9; 95% CI: 1.4-11) but not other obstetric events increased the risk for pelvic floor injury. Heavy smoking (≥ 20 pack-years) was associated (P=0.052) with external sphincter atrophy. CONCLUSIONS: State-of-the-art imaging techniques reveal pelvic floor injury or abnormal anorectal motion in a minority of community women with FI. Internal sphincter injury and reduced perineal descent during defecation are independent risk factors for FI. In addition to grades 3-4 episiotomy, smoking may be a potentially preventable, risk factor for pelvic floor injury.
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