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ORIGINAL RESEARCH |
From Department of Obstetrics and Gynecology, University of California Davis School of Medicine, Sacramento, California; and Health Information Solutions, Redwood City, California.
Address reprint requests to: Victoria L. Handa, MD, Department of Obstetrics and Gynecology, Johns Hopkins University School of Medicine, 600 North Wolfe Street, Harvey 319, Baltimore, MD 21287.
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ABSTRACT |
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 ABSTRACT MATERIALS AND METHODSRESULTSDISCUSSIONREFERENCES |
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METHODS: A population-based, retrospective study of over 2 million vaginal deliveries at California hospitals was performed, using information from birth certificates and discharge summaries for 1992 through 1997. We excluded preterm births, stillbirths, breech deliveries, and multiple gestations. The main outcome measure was obstetric anal sphincter laceration (third and fourth degree).
RESULTS: The frequency of anal sphincter lacerations was 5.85% (95% confidence interval [CI] 5.82, 5.88), decreasing significantly from 6.35% (95% CI 6.27, 6.43) in 1992 to 5.43% (95% CI 5.35, 5.51) in 1997 (P < .01). Using logistic regression analysis, we identified primiparity as the dominant risk factor (odds ratio [OR] for women with prior vaginal birth 0.15; 95% CI 0.14, 0.15). Birth weight over 4000 g was also highly significant (OR 2.17; 95% CI 2.07, 2.27). Lacerations occurred more often among women of certain racial and ethnic groups: Indian women (OR 2.5; 95% CI 2.23, 2.79) and Filipina women (OR 1.63; 95% CI 1.50, 1.77) were at highest risk. Episiotomy decreased the likelihood of third-degree lacerations (OR 0.81; 95% CI 0.78, 0.85), but increased the risk of fourth-degree lacerations (OR 1.12; 95% CI 1.05, 1.19). Operative delivery increased the risk of sphincter laceration, with vacuum delivery (OR 2.30; 95% CI 2.21, 2.40) presenting a greater risk than forceps delivery (OR 1.45; 95% CI 1.37, 1.52).
CONCLUSION: Anal sphincter lacerations are strongly associated with primiparity, macrosomia, and operative vaginal delivery. Of the modifiable risk factors, operative vaginal delivery remains the dominant independent variable.
As maternal and fetal mortality have declined over the past century, increased attention has been focused on the morbidity of childbirth. A recent survey of female obstetricians in Britain1 found that 31% would prefer elective cesarean delivery to minimize long-term maternal sequelae of vaginal delivery, such as urinary and anal incontinence. Such concerns are creating new controversies in women’s health.
The prevalence of anal incontinence in women is strongly associated with obstetric history and more specifically with obstetric lacerations of the anal sphincter. Even with immediate diagnosis and repair of sphincter lacerations, 40–50% of women report subsequent anal incontinence.2–4 Because recognition and repair of lacerations do not reliably prevent these sequelae, prevention is paramount.
The epidemiology of obstetric anal sphincter laceration is incompletely understood. This complication has been reported in 2.2% to 19% of vaginal births.5–8 Factors that have been associated with sphincter lacerations include primiparity,5,7,9,10 birth weight,5–9,11 episiotomy,5–11 and forceps delivery.5,6,8,10,12 Associations with race6,7 have also been suggested. Prior studies have been characterized by relatively small sample size and have been performed primarily at teaching hospitals, potentially limiting generalizablity.
The purpose of this study was to estimate the frequency of anal sphincter laceration in a large, heterogeneous population and to identify risk factors for this obstetric complication. Our goal was to identify modifiable risk factors and strategies for prevention.
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MATERIALS AND METHODS |
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We studied all vaginal deliveries between 1 January 1992 and 31 December 1997, excluding breech deliveries, preterm deliveries, multiple gestations, and stillbirths. The outcome of interest was injury to the anal sphincter, including both third- and fourth-degree sphincter lacerations. A third-degree tear is defined as a perineal laceration involving the anal sphincter. A fourth-degree tear is defined as a laceration that involves the anal sphincter and the rectal mucosa. Because most prior studies of laceration have not distinguished between third- and fourth-degree lacerations,5–9 we considered them as a single outcome.
A number of independent variables were examined for their association with anal sphincter lacerations. Demographic variables of interest included maternal age, race, education, and insurance type (private insurance, Medicaid, health maintenance organization, self-insured, and all other types of insurance). We also examined parity, which was classified into four categories: women delivering their first child ("primiparous"), women delivering their second child with a history of prior cesarean delivery ("prior cesarean only"), women with a history of one or more previous vaginal deliveries but no prior cesarean deliveries ("multiparous"), and women with at least two prior deliveries and a history of cesarean delivery ("multiparous with prior cesarean").
Obstetric variables included macrosomia (birth weight greater than 4000 g), maternal diabetes, postdates pregnancy, abnormalities of the first stage of labor, prolonged second stage of labor, shoulder dystocia, prior cesarean delivery, and fetal distress. We also examined labor interventions (induction of labor, epidural anesthesia, episiotomy, forceps delivery, and vacuum delivery). The type of episiotomy (midline or mediolateral) was not specified.
We determined laceration rates for each study year. The Cochran-Armitage trend test13 was used to examine changes over time in laceration rates and obstetrical interventions. We first used bivariate descriptive statistics to identify characteristics associated with lacerations. For each apparent association, we calculated odds ratios (OR) and two-tailed 95% confidence intervals (CI). We then used logistic regression to identify statistically significant associations while controlling for possible confounding variables. For each independent variable, we obtained OR and two-tailed 95% CI. We performed separate logistic regressions for each year to examine changes in associations over time.
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RESULTS |
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2: 19.38; P < .001; Figure 1
).
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characterizes the study population and summarizes the results of bivariate analyses. The most striking finding was the strong association between sphincter laceration and first vaginal birth. Compared with nulliparous women, multiparas had one-sixth the risk of sphincter laceration (OR 0.14; 95% CI 0.13, 0.14). Women with abnormal labor or shoulder dystocia were also at markedly increased risk of sphincter laceration. Strong associations were observed for several obstetric interventions, including labor induction, episiotomy, and forceps or vacuum delivery. Epidural anesthesia was recorded in only 3.3% of all deliveries (69,642 cases), suggesting probable undercoding of this procedure at the time of discharge. Because of potential undercoding, this variable was excluded from further analysis.
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. Again, the largest independent protective effect was multiparity (OR 0.15; 95% CI 0.14, 0.15). We also observed large differentials with respect to race-ethnicity, especially among women of Indian descent (OR 2.50; 95% CI 2.23, 2.79). Strong associations were noted for fetal macrosomia (OR 2.17; 95% CI 2.07, 2.27) and shoulder dystocia (OR 2.67; 95% CI 2.47, 2.89). Both forceps and vacuum deliveries were associated with an increased risk of sphincter laceration (OR 1.45, 2.30; 95% CI 1.37, 1.52 and 2.21, 2.40). Episiotomy was protective for sphincter laceration, with OR 0.89 (95% CI 0.86, 0.92). However, in a separate analysis (results not shown), we found that episiotomy increased the likelihood of fourth-degree laceration (OR 1.12; 95% CI 1.05, 1.19), while decreasing the likelihood of third-degree laceration (OR 0.81; 95% CI 0.78, 0.85).
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, with the exception of the OR associated with operative deliveries. Figure 2 illustrates changes over time in the association between sphincter lacerations and operative deliveries. From 1992 to 1997, there was a significant increase in the OR for vacuum delivery and a decrease in the OR for forceps delivery. There was a simultaneous decline in the incidence of forceps delivery and increase in the incidence of vacuum delivery (Figure 3). The incidence of episiotomy significantly decreased over time, from 41.6% (95% CI 41.4, 41.7) in 1992 to 35.3% (95% CI 35.1, 35.4) in 1997 (Cochran-Armitage trend test P < 0.01).
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DISCUSSION |
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Our data revealed some surprising findings regarding modifiable risk factors for obstetric sphincter lacerations. The effect of episiotomy was the most unanticipated finding, in that this procedure was associated with a 10% decrease in sphincter laceration. Since the early 1980s, several retrospective case-control studies suggested that episiotomy independently increases sphincter lacerations, with OR as high as 8.9.7 We observed a significant decrease in the use of episiotomy over time and speculate that obstetricians and others are avoiding episiotomy in women perceived to be at increased risk of complex lacerations. This may be responsible for the apparent protective effect of episiotomy. However, we cannot exclude the possibility that episiotomy is less consistently documented (or coded) in the setting of a laceration. If the physician does not document an episiotomy in this setting (or if the episiotomy is not coded at hospital discharge), the result would be an apparent weakening of the association between episiotomy and laceration. This is a potential weakness of this study design.
Our findings indicate that episiotomy may decrease third-degree but increase fourth-degree lacerations. We speculate that episiotomy may cause a third-degree laceration to extend to the rectal mucosa. Because some aspects of continence may be more severely compromised by fourth-degree lacerations,3 our data do not lead us to recommend a more liberal use of episiotomy.
We found an increased risk of laceration with both forceps and vacuum deliveries. This effect was relatively modest, however. We observed an OR of 1.4 for forceps delivery, in contrast to published reports estimating that sphincter lacerations increase seven to eight times with forceps.5,6 We speculate that prior reports have affected obstetric practice in California, with obstetricians and others avoiding forceps delivery among women perceived to be at increased risk of sphincter lacerations. Over 5 years, the incidence of forceps delivery decreased, whereas the incidence of vacuum delivery increased, consistent with national trends.14 As vacuum deliveries have apparently replaced some forceps deliveries in California, there has been an observed increase in the association between sphincter lacerations and vacuum delivery. We speculate that vacuum deliveries are being substituted for forceps among women believed to be at high risk for perineal trauma.
Our results agree with prior reports suggesting a strong association between sphincter laceration and increased birth weight.5,7,8 This association is presumably due to the mechanical stress of delivering a large baby. Other factors that may reflect disproportion between the size of the baby and the maternal pelvis include shoulder dystocia, labor abnormalities, and prolonged second stage of labor. Our findings suggest that these obstetric diagnoses are all strongly associated with sphincter laceration.
Racial differences in the incidence of obstetrical lacerations have been previously reported.7 The increased risk of laceration among Asian women, Filipinas, and Indian women was striking in our study. Possible explanations for our observations include differences in body type7 and variations in perineal anatomy.15 We were not able to control for maternal height and weight in this model and these may confound apparent racial differences.
Although this study is based on a large, heterogeneous population, the use of coded discharge data can be criticized. Less critical diagnoses may be omitted in complex cases. Documentation and data collection methods are not standardized, and coding practices may vary. One example in our data set is the apparent undercoding of epidural anesthesia. Prior hospital-based studies have suggested that epidural anesthesia is not independently associated with sphincter laceration.12 Therefore, we do not feel that the lack of data on this procedure is a significant source of bias in our results. However, it does raise the question of whether other misclassifications could affect apparent associations. To assess the validity of the coding of sphincter lacerations, data were obtained from an independent, blinded review of a stratified sample of cases in this database (personal communication, 2001, P. S. Romano, University of California Davis, Sacramento, CA). The sensitivity and positive predictive value of coding for lacerations were 90.3% and 91.5%. These findings are reassuring. Nevertheless, accurate coding is dependent on accurate documentation in the medical record.
Another limitation of this study is the possibility that important risk factors may be missing from the model. For example, we were unable to control for the experience and training of the birth attendant, measures of maternal body type, and other obstetrical interventions (such as maternal position at the time of delivery and the use of perineal massage or fundal pressure). These interventions may influence the risk of lacerations.7,11,16–18
Our data suggest that anal sphincter lacerations are decreasing but remain a concern, especially for women undergoing a first vaginal birth. Observed trends in the use of episiotomy and forceps delivery suggest that the obstetric community may be responding to concerns about these procedures. The majority of risk factors for sphincter lacerations, such as parity and birth weight, are not modifiable. Operative delivery remains the dominant modifiable independent variable.
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Footnotes |
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Received November 30, 2000. Received in revised form April 9, 2001. Accepted April 12, 2001.
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REFERENCES |
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2. Sorensen SM, Bondesen H, Istre O, Vilmann P. Perineal rupture following vaginal delivery. Long-term consequences. Acta Obstet Gynecol Scand 1988;67:315–8.[Medline]
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6. Robinson JN, Norwitz ER, Cohen AP, McElrath TF, Lieberman ES. Episiotomy, operative vaginal delivery, and significant perineal trauma in nulliparous women. Am J Obstet Gynecol 1999;181:1180–4.[Medline]
7. Green JR, Soohoo SL. Factors associated with rectal injury in spontaneous deliveries. Obstet Gynecol 1989;73:732–8.
8. Peleg D, Kennedy CM, Merrill D, Zlatnik FJ. Risk of repetition of a severe perineal laceration. Obstet Gynecol 1999;93:1021–4.
9. Buchhave P, Flatow L, Rydhstroem H, Thorbert G. Risk factors for rupture of the anal sphincter. Eur J Obstet Gynecol Reprod Biol 1999;87:129–32.[Medline]
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12. Robinson JN, Norwitz ER, Cohen AP, McElrath TF, Lieberman ES. Epidural analgesia and third- or fourth-degree lacerations in nulliparas. Obstet Gynecol 1999;94: 259–62.
13. Margolin BA. Test for trend in proportions. In: Kotz S, Johnson NL, eds. Encyclopedia of statistical sciences. Volume 9. New York: John Wiley & Sons, 1988:334–6.
14. Curtin SC, Park MM. Trends in the attendant, place, and timing of births, and the use of obstetric interventions: United States, 1989–97. National Vital Statistics Reports 1999;47:1–12.
15. Zacharin RF. "A Chinese anatomy"—the pelvic supporting tissues of the Chinese and Occidental female compared and contrasted. Aust N Z J Obstet Gynecol 1977;17:1–11.
16. Shipman MK, Boniface DR, Tefft ME, McCloghry F. Antenatal perineal massage and subsequent perineal outcomes: A randomised controlled trial. Br J Obstet Gynaecol 1997;104:787–91.[Medline]
17. Labrecque M, Eason E, Marcoux S, Lemieux F, Pinault J, Feldman P, et al. Randomized controlled trial of prevention of perineal trauma by perineal massage during pregnancy. Obstet Gynecol 1999;180:593–600.
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