Anal sphincter disruption common with forceps-assisted vaginal delivery [Classics Series]

1. The anal sphincter was disrupted in 80% of forceps-assisted vaginal deliveries and 35% of spontaneous vaginal deliveries.

2. Sphincter injury occurred only in the setting of an episiotomy or perineal laceration.

Original Date of Publication: December 1993

This study summary is an excerpt from the book 2 Minute Medicine’s The Classics in Medicine: Summaries of the Landmark Trials, 2e (The Classics Series).

Study Rundown: Vaginal delivery and operative vaginal delivery are associated with lower overall morbidity and mortality compared to cesarean delivery. However, vaginal delivery is associated with a higher risk of pelvic floor dysfunction, including morbidities such as anal incontinence that can greatly impair quality of life. As of the 1990s, existing research on anal sphincter dysfunction after vaginal delivery was limited by retrospective design that precluded assessment of chronology and causality. As such, whether anal incontinence following vaginal delivery occurred as the result of obstetrical trauma or was caused by a progressive denervation of the anal sphincter muscles following occult pudendal nerve injury in labor remained unknown. The development of anal endosonography, which assesses both anal sphincter integrity and neurophysiologic function, permitted diagnosis of anal sphincter injuries in real time. Authors of the present work used this new technology to assess the integrity of the external anal sphincter before and after delivery to determine the incidence of mechanical and neurological trauma affecting the anal sphincter.

This cohort study was the first to prospectively evaluate the integrity and function of the anal sphincter before and after vaginal delivery. Findings identified a moderately common incidence of sphincter disruption with spontaneous vaginal delivery and a high incidence of disruption with forceps-assisted vaginal delivery. Further, results demonstrated that the majority of anal sphincter trauma occurred with the first vaginal delivery. Strengths of the investigation included assessment of structural integrity and neurophysiologic function by various modalities (anal endosonography, manometry and perineometry), stratification of outcomes by parity, and a similar proportion of black and white women enrolled. Future investigations would go on to confirm that forceps-assisted vaginal delivery and episiotomy are strong risk factors for high-order perineal lacerations and anal sphincter disruption.

Please click to read study in NEJM

In-Depth [prospective cohort]: A total of 202 consecutive pregnant women including both nulliparous (n = 135) and parous (n = 67) women were examined during the last 6 weeks of pregnancy and reevaluated 6 to 8 weeks after delivery. Anal sphincter structural integrity and neurophysiologic function were assessed with anal endosonography, manometry, perineometry, and pudendal nerve motor latency. Primary outcome was a defect in the internal or external anal sphincter. Secondary outcomes included symptomatology, such as stool, and fecal incontinence.

The incidence of anal sphincter defect at 6 weeks postpartum was 35% in primiparous women. In parous pregnant women, 40% had a pre-existing anal sphincter defect and the incidence increased only 4% after delivery, implying that the majority of sphincter damage occurs with the first delivery. Among women who underwent forceps-assisted vaginal delivery (n = 10), 8 women (80%) experienced anal sphincter injury compared to 0 out of 5 sphincter injury after vacuum-assisted deliveries. All external anal sphincter injuries occurred in the setting of episiotomy or laceration. Sphincter defects were strongly associated with bowel symptoms (p < 0.001).

Sultan AH, Kamm MA, Hudson CN, Thomas JM, Bartram CI. Anal-sphincter disruption during vaginal delivery. The New England Journal of Medicine. 1993;329(26):1905-11.

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