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    Grand Rounds: Managing future pregnancies after a severe perineal laceration

    What do you tell a pregnant patient with a previous third- or fourth-degree tear, for whom another vaginal delivery raises the risk of further injury? Can some women even safely have a trial of labor? Diagnose occult tears with ultrasound, advise these experts—and use it to assess the anal sphincters of all incontinent women.

    The advice you give a pregnant patient who has suffered an anal sphincter laceration during a previous delivery can have a critical impact on her quality of life. With another vaginal birth, she's more likely to suffer a repeat anal sphincter tear and worsening symptoms of anal incontinence. Sexual dysfunction may also be at stake. Despite all this, there are no easy answers, because the best way to manage a subsequent pregnancy of a woman with a previous tear is controversial.

    Free Online CME
    Sphincter tears resulting from vaginal delivery occur in 0.7% to 19.3% of births, mostly during a first pregnancy.1-4 How do you advise the many patients who become pregnant again? Our goal here is to review the classification and complications of anal sphincter lacerations, as well as outcomes following subsequent vaginal delivery. We'll also present management strategies for future pregnancies.

    Figure 1. Third-degree perineal laceration
    Anatomical knowledge of the anorectal canal is essential. The canal is surrounded by a complex tube of muscle fibers composed of the external and internal sphincters. The striated muscles of the external sphincter are under voluntary control, and are responsible for the squeeze tone of the rectal canal. The smooth muscle of the internal sphincter, on the other hand, maintains resting tone and is responsible for minute-to-minute fecal continence. Both muscle groups overlap for a distance of 2 cm and extend 4 cm up the canal. The external sphincter is attached to the perineal body and is surrounded by the puborectalis muscle.

    Figure 2. Fourth-degree perineal laceration
    Although both sphincters are important in maintaining continence, laceration classification is based only on the extent of injury to the external anal sphincter. Third-degree lacerations include complete or partial laceration of the external sphincter—with or without internal sphincter laceration (Figure 1), whereas fourth-degree lacerations include complete laceration of both sphincters with extension into the rectal mucosa (Figure 2). [Anal continence doesn't completely depend on intact sphincters; also important are intact neuromuscular function, including a functioning puborectalis muscle and pudendal nerve. This is supported by the fact that some women with sphincter lacerations remain continent.]

    Figure 3. A normal finding on translabial U/S
    Anal sphincter lacerations are further classified into "overt" or "occult" lacerations. Overt lacerations are identified and repaired at the time of delivery, while occult lacerations can only be diagnosed by ultrasound or magnetic resonance imaging. Occult lacerations, which are most commonly diagnosed by U/S, can occur beneath an intact perineum or in the presence of less severe second- or first-degree tears in up to 35% of first-time deliveries.5 (Figure 3 shows a normal finding on translabial U/S, while Figures 4 and 5 show occult lacerations using translabial and transanal U/S respectively.)

    [Five key risk factors of severe lacerations are: (1) Midline episiotomy, (2) Forceps or vacuum delivery (vacuum being less traumatic than forceps), (3) Asian ancestry, (4) High birthweight, and (5) First birth.4,6,7]

    Rebecca G. Rogers, MD
    Dr Rogers is Associate Chair for Clinical Integrations and Operations, Dell Medical School, The University of Texas at Austin.
    Husam Abed, MD
    DR. ABED is Clinical Faculty, Division of Female Pelvic Medicine and Reconstructive Surgery, University of New Mexico, Albuquerque, N.M.


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