Risk Factors Associated with Anal Sphincter Tears
Risk Factors Associated with Anal Sphincter Tears
abstract & commentary
Synopsis: In nulliparous women, perineal protection,visualization of the perineum, and high birth weight had a greater effect than in parous women.
Source: Samuelsson E, et al. Br J Obstet Gynaecol 2000;107:926-931.
To determine the intrapartum risk factors for anal sphincter tears, Samuelsson and colleagues performed a prospective observational study of 2883 consecutive vaginal deliveries between 1995 and 1997 at a single hospital in Sweden. Third-and-fourth degree lacerations were combined in the statistical analysis. The deliveries were performed by midwives unless vacuum or forceps were required. An anal sphincter tear occurred in 95 women (3.3%), 66 nulliparous, and 29 multiparous patients. Mediolateral episiotomies were performed in 16.6% of nulliparous women, and 5.3% of parous women. Few midline episiotomies were done. Nearly 10% of the nulliparous women were delivered by vacuum extraction while less than 3% of the parous women underwent this form of delivery. Only five forceps deliveries were performed in the entire study population. Epidural anesthesia was administered to nearly 45% of nulliparous, but less than 15% of parous patients. Most women delivered in the semi-recumbent or lateral position. Multiple regression analysis demonstrated that an infant birth weight greater than 4000g and lack of visualization of the perineum significantly increased the risk of an anal sphincter tear; while minimal edema of the perineum, pushing for less than 30 minutes, nulliparity, and manual perineal protection (e.g., the Ritgen maneuver), significantly lowered the risk of anal sphincter tear. In nulliparous women, perineal protection, visualization of the perineum, and high birth weight had a greater effect than in parous women.
Samuelsson et al believe that this information may be helpful in developing strategies to reduce perineal trauma.
Comment by Steven G. Gabbe, MD
In recent years, retrospective and now prospective studies have emphasized the effect of vaginal delivery on urinary and fecal continence. This important investigation from Sweden used a carefully designed protocol to document all of the factors which may lead to disruption of the anal sphincter at the time of birth. The practice of obstetrics certainly differs in Sweden, with most of the deliveries performed by midwives, limited use of episiotomy and, when it is used, mediolateral episiotomy is preferred, most women delivering without epidural anesthesia, and 30-45% giving birth in positions other than the dorso-lithotomy position. Nevertheless, the data may help obstetricians in this country as they seek to reduce pelvic floor trauma. While there are several factors that cannot be directly influenced by the obstetrician, such as infant birth weight and parity, others, including perineal protection, should be used. It is important to remember that the anal sphincter tears reported in this study were those that could be identified on gross visual inspection. It is likely that many more women had sphincter injuries that would have been found with anal endosonography.
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