FIGURE 27-13 1. First-degree perineal laceration: injury to only the vaginal epithelium or perineal skin. 2. Second-degree laceration: injury to perineum that spares the anal sphincter complex but involves the perineal muscles, which are the bulbospongiosus and superficial transverse perineal muscles. 3a.Third-degree laceration: <50 percent of the external anal sphincter (EAS) is torn. 3b.Third-degree laceration: >50 percent of the EAS is torn, but the internal anal sphincter (lAS) remains intact. 3c.Third-degree laceration: EAS and lAS are torn.
4. Fourth-degree laceration: the perineal body, entire anal sphincter complex, and anorectal mucosa are lacerated. (Reproduced with permission from Kenton K, Mueller M: Episiotomy and obstetric anal sphincter lacerations. In Yeomans ER, Hoffman BL, Gilstrap LC III, et al (eds):
Cunningham and Gilstrap's Operative Obstetrics, 3rd ed. New York, McGraw-Hili Education, 201o7.) hird-and fourth-degree lacerations are considered obstetrical anal sphincter injuries (OASIS), and their combined incidence varies from 0.5 to 5 percent (Blondel, 2016; Friedman, 2015).
ity, midline episiotomy, persistent OP position, operative vaginal delivery, Asian race, short perineal length, and increasing fetal birthweight (Ampt, 2013; Dua, 2009; Gurol-Urganci, 2013;
Landy, 2011). Mediolateral episiotomy is protective in most, but not all, studies Ganga, 2014; Raisanen, 2011; Shmueli, 2016).
Morbidity rates rise as laceration severity increases. Compared with simpler lacerations, anal sphincter injuries are associated with greater blood loss and puerperal pain. Wound disruption and infection rates are other risks (Goldaber, 1993; Lewicy-Gaupp, 2015). Stock and coworkers (2013) reported that approximately 7 percent of 909 OASIS lacerations had complications. Long term, anal sphincter injuries are linked with approximately doubled rates of fecal incontinence compared with vaginl delivery without OASIS (Evers, 2012; Gyhagen, 2014). Data on long-term dyspareunia are limited, and rates are increased in some but not all studies (MoS, 2008; Otero, 2006; Salim, 2014; Sundquist, 2012).
To ensure appropriate repair, identiication and correct categorization is essential. Diagnosis rates of OASIS improve with clinical experience (ndrews, 2006). Intrapartum endoanal ultrasound, performed in research studies, also boosts detection, and rates of clinically occult tears in primiparas range from 6 to 12 percent (Corton, 2013; Faltin, 2005; Ozyurt, 2015). hat said, few data currently support routine intrapartum endoanal sonography, and the American College of Obstetricians and Gynecologists (20 16b) does not recommended i t (Walsh, 2015).