Sphincter injuries and anal incontinence after vaginal delivery : a clinical and physiological study

Abstract

Objective: To investigate the frequency and degree of anal incontinence after vaginal delivery in primiparous women, to determine risk factors for obstetric sphincter tears and to evaluate outcome of primary repair, to evaluate perineal body measurement (PBM) in patients with obstetric sphincter injuries, to study anal sphincter morphology and function before and after delivery, and to evaluate primiparous women who had sustained a sphincter tear or developed anal incontinence after delivery.

Methods: Questionnaires regarding anal incontinence before pregnancy, at five and nine months after delivery were used. Risk factors for anal sphincter tears were calculated by multiple logistic regression. Endoanal ultrasonography (EAUS), anorectal manometry, and electrophysiology were used.

Results: At nine months postpartum, 1% of the women had symptoms of fecal incontinence and 26% of involuntary flatus. 'Me majority had infrequent symptoms. Incontinence was more common in women who sustained a sphincter tear at delivery. Sphincter tears were associated with nulliparity, postmaturity, fundal pressure, midline episiotomy, and fetal weight. Forty-one percent of women with repaired sphincter tears suffered from fecal and/or gas incontinence at nine months. In incontinent patients, PBM was 6±2 mm compared with 12±3 mm in asymptornatic subjects (p<0.001). Ninetythree percent of patients had PBM < 10 mm and 70% of asymptomatic subjects had PBM >10 mm. Digital delineation of the perineal body at EAUS improved the visualization of sphincter lesions in 74% of the patients. In nulliparous women, all physiological investigations were normal before delivery. Clinical sphincter tears occurred in 15% of these women. After delivery, ultrasonography revealed disruptions in the external anal sphincter in 16% but none had disruption of the internal anal sphincter. At follow-up, 70% of women who sustained a clinical sphincter tear at delivery had injuries anteriorly in the midanal canal at EAUS, 4% had decreased resting pressure and 50% decreased squeeze pressure at manometry, and 19% had pathological pudendal latency and 25% pathological fiber density at electrophysiology. Of women assessed due to anal incontinence after the delivery, 44% had injuries anteriorly in the midanal canal at EAUS, all had normal resting pressure and 19% had a decreased squeeze pressure at manometry, and 46% had pathological pudendal latency and 29% pathological fiber density at electrophysiology.

Conclusions: Infrequent involuntary flatus was common after vaginal delivery in primiparous women and only a few women suffered from frank fecal incontinence. Several risk factors for sphincter tear were identified. Sphincter tear at vaginal delivery is thus a serious complication and identified risk factors should be considered. Anal incontinence should explicitly be inquired at follow-up after delivery. Digital delineation of the perineal body at EAUS improved the visualization of sphincter lesions. PBM was performed without difficulty and was a good predictor of anterior sphincter lesions. Anal sphincter injuries at vaginal delivery were often inadequately diagnosed and primary repair frequently resulted in persisting defects in the anal sphincter. It is concluded that anatomical injuries to the anal sphincter plays an important role in the development of anal incontinence after delivery, but a significant proportion of symptomatic women also demonstrate neurological impairment.