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Original Research

Risk Factors for Anal Sphincter Tear in Multiparas

DiPiazza, DeAnn MD; Richter, Holly E. PhD, MD; Chapman, Victoria RN, MPH; Cliver, Suzanne P. BA; Neely, Cherry; Chen, Chi Chiung MD; Burgio, Kathryn L. PhD

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doi: 10.1097/01.AOG.0000217696.25548.ff
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Pelvic floor morbidity, including urinary incontinence (UI), fecal incontinence (FI), and prolapse, has been associated with vaginal delivery.1–12 Prevalence of stool incontinence has been reported to be 3% after vaginal birth, while the rate of flatal incontinence was 37%.1,2,13,14 Stool incontinence is even more common after an anal sphincter tear, affecting 8–40% of women.1,13–15 Multiparous women have a higher risk of urinary and fecal incontinence symptoms than primiparous women, as many have already sustained injury to the pelvic floor with a previous delivery.7,16–18

Risk factors commonly cited for obstetric sphincter tear are primiparity, episiotomy, macrosomia, operative delivery, and shoulder dystocia.4,11,13,19–23 The prevalence of anal sphincter tears in general is approximately 6%20 but has been reported to be as high as 10%.21 However, fewer studies have reported the occurrence of sphincter tears in multiparous women, in whom rates range from 1% to 4%.24–26

Risk factors associated with sphincter tear in primiparous deliveries are reasonably well characterized, but only seven studies have specifically addressed risk factors for sphincter tears in the multiparous patient.24–30 These studies have been large cohort studies using databases with limited variables. Most have revealed an increased risk of anal sphincter tears with a history of previous third- and fourth-degree tear but have not detailed other risk factors.24–30

The objective of this case–control study was to examine a spectrum of variables to identify maternal, newborn, and labor risk factors associated with sphincter tear in multiparous patients.


Institutional Review Board approval was obtained. Patient records were identified using an obstetric automated record system of deliveries from University Hospital between 1992 and 2004. Cases were chosen by identifying all multiparous women who had sustained a third- or fourth-degree tear in the index pregnancy, had two or more consecutive vaginal deliveries with no previous cesarean delivery, and gestational age more than 20 weeks at the time of delivery. Breech deliveries were excluded.

Control subjects were randomly selected from all other multiparous women with no prior cesarean delivery and category matched for year of delivery. After identifying patients in an obstetric automated record system, the medical records for both index and previous pregnancies were individually reviewed by the authors. A broad spectrum of variables was analyzed as possible risk factors for sphincter tear including newborn, labor, and maternal characteristics. A history of sphincter tear in any prior delivery was obtained by reviewing previous pregnancy charts.

Crude and adjusted odds ratio with 95% confidence intervals were calculated. All significant risk factors (P < .05) identified were then placed in two stepwise logistic regression models to identify factors most associated with tear and to adjust for potential confounding variables. The first model included information from the index pregnancy for both cases and controls. The second model was an exploratory model and included history from previous pregnancies. This model was limited by availability of prior pregnancy charts. Analysis was performed using SAS 9.1 (SAS Institute, Cary, NC).


Review of obstetric automated record system records from 1992 to 2004 determined that 18,779 multiparous women delivered vaginally without a history of cesarean delivery. Of these patients, 240 were identified in the obstetric automated record system as having sustained a third- or fourth-degree tear. Review of the medical charts revealed that only 145 of the original 240 sustained a sphincter tear and had no history of cesarean delivery. By using the obstetric automated record system, 287 controls with no history of cesarean delivery were identified and category matched for year of delivery. After chart review, several patients did not match inclusion criteria or their charts were not available, leaving 139 control subjects. Descriptive characteristics are shown in Table 1. Fifty-one percent (51%) of all patients were African American, 41% white, 4% Hispanic, and 4% other. Data for the index pregnancy revealed that cases were more likely to be older, of greater gestational age and lower parity, have a longer interval from previous pregnancy to current pregnancy, have a prolonged length of labor time, and have newborns who weighed more (Table 1).

Table 1
Table 1:
Descriptive Characteristics of Index Pregnancies

Univariate analysis identified a total of 15 maternal, fetal, and labor variables as significantly associated with anal sphincter tears (Table 2). Interestingly, vacuum delivery, epidural anesthesia, and position of fetal vertex were not associated with increased risk.

Table 2
Table 2:
Univariate Analysis and Risk Factors for Sphincter Tear

Two stepwise logistic regression models were constructed. The first model (n = 228) included information only from the index pregnancy for both cases and controls. Six subjects were missing data on forceps use, 1 on dystocia, 8 on marital status, and 45 were missing length of first stage of labor. Four variables were significantly associated with increased risk of sphincter tear: episiotomy, shoulder dystocia, forceps delivery, and being married (Table 3). The regression analysis was repeated with the variable “length of first stage of labor” removed, increasing the number from 228 to 271. There was no change in significance level of the remaining variables. The second model (n = 118) was an exploratory model, as it was limited by availability of prior pregnancy charts (46% of case and 70% of control charts available). In this model, previous sphincter tear was a significant factor for a tear with the index delivery, in addition to episiotomy, shoulder dystocia, forceps delivery and prolonged second stage of labor (Table 4).

Table 3
Table 3:
Multivariable Logistic Regression Model (Index Pregnancy Variables)
Table 4
Table 4:
Multivariable Logistic Regression Model (Index and Previous Pregnancy History)


We have shown that a number of maternal, labor, and newborn variables of both the index and previous pregnancies may be associated with an increased risk of anal sphincter tear in the multiparous woman. Many reports have documented risk factors for sphincter tear in the nulliparous patient.2,16,19,20,22–24 Interestingly, the factors associated with multiparous sphincter tears are similar to those of the nulliparous patient, including forceps delivery, prolonged second stage of labor, and episiotomy.16,19,20,22–30 This may reflect common labor practices for both the nulliparous and parous women.

The current literature describing risk factors for sphincter tear in multiparous women includes seven other studies.24–30 The most common risk factors identified were a history of prior tear, forceps delivery, episiotomy, and birth weight > 4,000 g,24–30 which is consistent with risk factors identified in our study. In addition, Spyslaug et al25 also identified prolonged labor greater than 24 hours or second stage of labor greater than 60 minutes as a risk factor for sphincter tear, and Elfaghi et al26 found increasing maternal age as risk factor for tear.

Episiotomy was the risk factor most strongly correlated with sphincter tear in our study. Episiotomy has not been found to be protective to the pelvic floor as had been previously thought,8,20,22,23,30,31 and its use should not be routine. As with episiotomy, forceps delivery was also very strongly associated with sphincter tear. Operative delivery, while often indicated, is a risk factor for sphincter tear, and practitioners may consider counseling patients before labor about operative vaginal delivery and its possible sequelae. Shoulder dystocia, while not predictable, often requires increased force on the pelvic floor or an episiotomy or proctoepisiotomy performed to extricate the fetus at the expense of potential traumatic perineal injury.

Because a woman has a “proven pelvis” does not mean that she is at decreased risk for a traumatic delivery. Obstetricians may consider counseling multiparous patients that a history of sphincter tear is a risk factor for a subsequent tear as found in our study and multiple others25–29 with subsequent increased risk for symptoms of fecal incontinence.1,7,13,17,18 Whether an elective cesarean delivery should be offered to these patients is unclear and controversial,8,16,21,32–34 as primary cesarean itself has not been shown to be totally protective against symptoms of fecal and urinary incontinence.16,32,33,35

Increasing length of second stage of labor as a risk factor for sphincter tear may be reflective of our propensity to hasten delivery by operative delivery or with the use of episiotomy. Two retrospective studies have shown that increased rates of operative deliveries, postpartum hemorrhage, and chorioamnionitis are associated with second stage of labor longer than 2 hours.36,37 Therefore, practitioners should consider not only the aforementioned maternal morbidity but also an increased risk of sphincter tear when counseling multiparous patients regarding continued pushing versus cesarean delivery during a prolonged second stage of labor.

Being married was associated with sphincter tear in multiparous women, a finding which has not been report in other studies. It is possible that being married is a marker for higher socioeconomic class, maternal age, or other factors not represented in our models. Of note, with the models adjusted for increased birth weight and maternal age, being married was still a significant risk factor. Future studies may need to more fully evaluate characteristics associated with being married.

This study differs from other multiparous risk factor studies in that we evaluated multiple maternal, fetal, and labor factors of the index and previous pregnancies. This is a heterogenous population including 51% African American, 40% white, and 4% Hispanics as compared with the most recent large studies of homogenous populations from Sweden and Norway.25,26 Furthermore, all variables were confirmed by a thorough chart review to alleviate potential inherent bias.

Limitations of this study include those associated with the use of an automated database where there may be miscoding at the time of data entry thereby missing or falsely identifying sphincter tears and other covariates; however, the charts of all index pregnancies and available prior pregnancies were reviewed by hand to minimize any discrepancies. Fifty percent of the past pregnancy charts were missing, which may have had an impact on the results.

In summary, multiparous patients with a history of vaginal delivery with an anal sphincter tear may be at risk for a recurrent tear. Furthermore, having an episiotomy, shoulder dystocia, second stage of labor greater than or equal to 1 hour, and forceps in a subsequent delivery may be associated with an increased risk of sustaining a tear. Recommendations for future pregnancy management would include minimizing the use of episiotomy and operative delivery with forceps. However, well-controlled prospective clinical studies are needed to determine if that would result in decreased risk for sphincter tear.


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© 2006 by The American College of Obstetricians and Gynecologists. Published by Wolters Kluwer Health, Inc. All rights reserved.