Abstract
Objective
To examine what effect the major modifiable risk factors for severe perineal trauma have had on the rates of this trauma over time.
Methods
A retrospective observational cohort study of singleton vaginal deliveries taken from a perinatal database for the period 1996 through 2006.
Results
A total of 46 239 singleton vertex vaginal deliveries met the inclusion criteria. Major risk factors for severe perineal trauma were increased maternal age (odds ratio [OR] 1.28, 95% confidence interval [CI] 1.1–1.5), non–African American ethnicity (OR 1.5, 95% CI 1.3–1.7), nulliparity (OR 4.8, 95% CI 4.11–5.6), fetal birth weight (OR 2.2, 95% CI 1.9–2.4), forceps (OR 8.3, 95% CI 5.4–10.8), vacuum (OR 2.9, 95% CI 1.9–4.4), and midline episiotomy (OR 5.7, 95% CI 5.0–6.4). Evaluation of the changes in rates of these factors over the study period revealed that decline in the rates of episiotomy and use of forceps accounted for a reduction in severe lacerations of more than 50%.
Conclusion
Reduction of severe perineal trauma by restricted use of the 2 modifiable clinical variables, episiotomy and forceps, is evident over time.
Keywords: Cesarean delivery, Episiotomy, Forceps, Severe perineal trauma, Trends
1. Introduction
Severe obstetric perineal trauma is thought to be the primary cause of fecal and flatus incontinence in young women [1,2]. The rate of clinically visible anal sphincter lacerations is estimated to be between 0.5% and 18% [3-5]. However, the actual rate of anal sphincter trauma is underestimated dramatically. Some studies have shown that occult sphincter tears are detectable in up to 35% of vaginal deliveries [3,6,7]. Even when severe perineal trauma is recognized and adequate primary repair is attempted immediately post partum, the outcome is often suboptimal as up to 59% of these women suffer from some form of anal incontinence, fecal urgency, and dyspareunia [3,8-10]. In addition, it has been demonstrated that 71% of women with late-onset fecal incontinence evidenced ultrasonographic anal sphincter defects thought to have occurred during vaginal delivery [11]. Although the association between anal sphincter tears and anal incontinence might not be direct, a possible reduction of the rate of anal sphincter injury during childbirth through knowledge, modification, or prevention of the key risk factors should be investigated.
Over the last 20 years many studies have attempted to isolate the risk factors for anal sphincter trauma. The results of these studies have indicated that midline episiotomy, operative vaginal delivery (particularly forceps delivery), macrosomia, shoulder dystocia, epidural anesthesia, occiput posterior presentation, prolonged second stage of labor, and nulliparity are major risk factors [2,12-14]. The aim of the present study was to evaluate data from our tertiary care institution to assess whether a reduction in the potentially modifiable risk factors for severe perineal trauma would result in a reduction in its rate.
2. Materials and methods
Data were extracted from the computerized perinatal database at our tertiary care teaching institution for the 11-year period from 1996 through 2006 for all singleton vaginal deliveries and maternal age, parity, race, marital status, epidural anesthesia, birth weight, newborn head circumference, use of midline episiotomy, operative vaginal delivery indication and type (forceps, vacuum), type of forceps (mid, low, outlet), and type of perineal laceration. Exclusion criteria were women who delivered at less than 24 weeks of gestation, women who had a multiple pregnancy, multiple births at the same institution, nonvertex presentation, stillbirth, operative delivery with both forceps and vacuum extraction, or cesarean delivery. Obstetric care providers at our institution included general obstetrics/gynecology and maternal-fetal-medicine attending physicians, interns and residents, and midwives. All deliveries by interns and residents were performed under the supervision of attending physicians. Repairs of episiotomies and severe perineal lacerations were performed by attending physicians or residents under the supervision of attending physicians.
The primary outcome variable was development of severe perineal injury, defined as either a third- or fourth-degree perineal laceration/extension. The classification of the degree of perineal tearing was based on the standard definitions used in American obstetric practice: third-degree laceration defined as perineal laceration involving the anal sphincter, and fourth-degree perineal laceration defined as an injury involving both the anal sphincter and the anorectal mucosa [15]. We used the smallest odds ratio of 1.2 for ethnicity from one of our previous studies [16] to obtain a sample size of 33 000; this provided 80% power to identify a 20% difference in anal sphincter trauma between women with and without clinically visible severe perineal lacerations, with a 2-sided 5% test of significance.
Validation analysis of the major risk factors for the development of severe perineal injury was performed using a random split-half method. Participants were randomly split into 2 independent datasets, training and validation, of approximately equal size (23 183 and 23 056 women, respectively) using a computer generated algorithm. Factors that best predicted anal sphincter trauma (P<0.1) were selected from the univariate analysis of the training dataset and entered into a stepwise multiple logistic regression to create a model (P<0.05). Using this model, we computed the probability of severe perineal laceration for the women in the validation dataset. Subsequently, a z-test was used to examine robustness versus shrinkage of performance of the model by comparing the areas under receiver operator characteristic curves for the predicted versus observed rates of severe perineal lacerations in the 2 datasets. This was done to measure how well the model from the training dataset predicted severe perineal trauma in the validation dataset. Large shrinkage would indicate that the model only worked well in the first or training dataset, whereas small shrinkage would indicate that the model was generalizable i.e. robust and therefore would validate the major risk factors for severe perineal trauma.
The continuous variables of age and neonatal weight were included in the analysis as categorical variables. The best discriminative cut-off points were 24 years for age and 3300 g for neonatal weight from the 2 respective receiver operator curves for predicted versus observed anal sphincter trauma in the training dataset. In addition, based on the results of previous studies, including our own, which demonstrated that women of African American descent had a significantly lower risk of anal sphincter tears than white, Hispanic, and Asian women, a dichotomous variable for ethnicity was created: African American and non–African American (Table 1). The impact of mediolateral episiotomy was evaluated together with midline episiotomy because the rate of mediolateral episiotomy was extremely low (Table 1) and the risk of severe perineal trauma, compared with midline episiotomy, was not significantly different.
Table 1. Demographic and obstetric characteristics of the women with and without anal sphincter lacerationa.
| Characteristics | No anal sphincter laceration (n=44 862; 97.02%) |
Anal sphincter laceration (n=1377; 2.98%) |
Univariate P value |
|---|---|---|---|
| Maternal age, y Missing (n=15) | 23.4 ± 6.0 | 24.7 ± 6.2 | <0.001 |
| Ethnic background | <0.001 | ||
| Black | 33 024 (73.6) | 837 (60.8) | |
| White and other | 11 443 (25.5) | 489 (35.5) | |
| Asian | 395 (0.9) | 51 (3.7) | |
| Missing (n=15) | |||
| Marital status | <0.001 | ||
| Married | 8466 (18.9) | 400 (29) | |
| Not married | 36 391 (81.1) | 977 (71) | |
| Missing (n=20) | |||
| Parity | <0.001 | ||
| Nulliparity | 15 336 (34.2) | 1088 (79) | |
| Multiparity | 29 497 (65.8) | 288 (21) | |
| Missing (n=45) | |||
| Gestational age, weeks | 38.7 ± 2.4 | 39.5 ± 1.6 | <0.001 |
| Neonatal weight, g | 3137 ± 577 | 3392 ± 477 | <0.001 |
| Missing (n=6) | |||
| Head circumference, cm | 33.5 ± 1.9 | 34.1 ± 1.7 | <0.001 |
| Missing (n=4496) | |||
| Length, cm | 49.7 ± 3.3 | 51.1 ± 2.6 | <0.001 |
| Missing (n=427) | |||
| Anesthesia | <0.001 | ||
| Epidural | 23 316 (52) | 952 (69.1) | |
| No epidural | 21 560 (48) | 425 (30.9) | |
| Missing (n=1) | |||
| Vaginal deliveries | <0.001 | ||
| Spontaneous | 42 701 (95.2) | 823 (59.8) | |
| Forceps | 1406 (3.1) | 406 (29.5) | |
| Vacuum | 755 (1.7) | 148 (10.7) | |
| Episiotomy | |||
| Midline | 2851 (6.4) | 722 (52.4) | <0.001 |
| Mediolateral | 43 (0.1) | 6 (0.4) | 0.34 |
Values are given as number (percentage) or mean ± SD unless otherwise indicated.
Finally, we evaluated what effect the validated major risk factors had on the rate of severe perineal trauma over time. Cesarean deliveries were separated into primary and repeat, examined in a separate descriptive analysis, and were then combined with all vaginal deliveries to evaluate the effect of various operative interventions on the rate of severe perineal trauma. Over the 11-year period we examined the changes in the monthly rates per 100 deliveries of the validated risk factors (nulliparity, maternal age, neonatal weight, ethnicity, vacuum and forceps deliveries, midline episiotomy) in addition to the other 2 factors (primary and repeat cesarean deliveries) on our service to estimate the contribution of these factors to the decline in rate of severe perineal laceration. Only statistically significant factors from a univariate analysis (P<0.1) were entered into multivariate linear regression analysis. Statistical analyses were carried out using SPSS 14.0 (SPSS, Chicago, IL, USA).
The study was approved by the Human Investigation Committee of the Wayne State University/Detroit Medical Center-Hutzel Hospital.
3. Results
Over the 11-year study period (1996–2006), 46 239 vaginal deliveries met the inclusion criteria and 13 321 cesarean deliveries (8258 primary and 5063 repeat) were performed at our tertiary care institution. Severe perineal trauma was experienced by 2.9% of women included in the study. Patient characteristics are given in Table 1.
Univariate analyses of the training dataset found that maternal age, nulliparity, race, marital status, gestational age, epidural anesthesia, birth weight, newborn head circumference, use of midline episiotomy, forceps, vacuum, and ethnicity were associated with severe perineal trauma. However, of these variables, only 7 (maternal age, ethnicity, nulliparity, forceps, vacuum extraction, and neonatal birth weight) were found to be the major risk factors for anal sphincter lacerations in multiple logistic regression analysis (Table 2). Using the training dataset model based on the above 7 variables, we computed the probability of severe perineal laceration for the women in the validation dataset. Minimal shrinkage was observed, indicating that the proposed model was robust and its results were generalizable (z-statistic 1.3, P=0.097). Thus, this statistical method allowed for validation of the 7 risk factors for severe perineal trauma.
Table 2. Results of multiple logistic regression analysis for training and validation datasets.
| Clinical variables | Training dataset (n=23 183) |
Validation dataset (n=23 056) |
|---|---|---|
| OR (95% CI) | OR (95% CI) | |
| Age, ≥24 yearsa | 1.4 (1.1–1.6) | 1.2 (1.1–1.5) |
| Ethnicity | 1.6 (1.3–1.9) | 1.4 (1.2–1.7) |
| Birth weight, ≥ 3300 gb | 2.2 (1.8–2.6) | 2.1 (1.8–2.5) |
| Episiotomy | 5.6 (4.7–6.7) | 5.8 (4.9–6.9) |
| Nulliparity | 4.5 (3.7–5.5) | 4.8 (3.9–5.8) |
| Forcepsc | 8.1 (5.9–10.1) | 8.5 (6.1–10.9) |
| Vacuumc | 2.9 (1.9–4.2) | 3.1 (1.9–4.5) |
Age: categorical age variable, ≥24 years of age, based on the best ROC cut-off point.
Birth weight: categorical neonatal birth weight variable, ≥ 3300g, based on the best ROC cut-off point.
Operative vaginal delivery that includes forceps and vacuum together.
The impact of the validated risk factors on the development of severe perineal trauma was examined by evaluating the changes in obstetric practice at our tertiary care institution. This was done because a randomized controlled trial of the second-stage interventions versus no intervention, or planned elective cesarean delivery versus vaginal delivery is not feasible at this time [17]. Specifically, we wanted to evaluate whether a reduction in the validated potentially modifiable factors would result in a reduction in the rate of severe perineal trauma. Evaluation of the 11-year trend in obstetric practice at our tertiary center resulted in finding more convincing inferences of causality between the modifiable factors in the model described above and severe perineal trauma. We noted a significant reduction in anal sphincter trauma from 5.4% in 1996 to 1.3% in 2006 and a dramatic drop in the rates of episiotomy and operative vaginal deliveries, with a concurrent overall increase in the rate of cesarean deliveries from 18.9% in 1995 to 29.4% in 2006 (Figures 1 and 2). In order to evaluate a change in the rate of anal sphincter trauma over time, we looked at the month-by-month changes in the rates of nulliparity, ethnicity, episiotomy, forceps and vacuum deliveries, primary and repeat cesarean deliveries, and in the mean maternal age and neonatal weight. No changes in the monthly rates of nulliparity, mean monthly maternal age, and mean monthly neonatal weight were observed over the 11-year period. The final model consisted of the following 4 factors: monthly rates of episiotomy, primary cesarean delivery, forceps, and repeat cesarean delivery. This model explained 70% of the variance in the decrease in the rate of severe perineal trauma. It confirmed that the reduction in anal sphincter lacerations was strongly associated with the fall in the rate of episiotomy (R2=48.7%), followed by a rise in the rate of primary cesarean delivery (R2=16.3%), with a concurrent reduction in the rate of forceps use and an increase in the rate of repeat cesarean delivery (Table 3). More than two-thirds of the explained variance was due to the fall in the rate of episiotomy and forceps which suggests what might be accomplished by reducing the number of operative interventions.
Figure 1.
Trends in the rates of severe perineal lacerations, primary and repeat cesarean deliveries, midline episiotomy, and operative vaginal delivery over the study period (per 100 vaginal deliveries)
Figure 2.
Trends in the rates of cesarean deliveries over the study period (per 100 deliveries)
Table 3. Factors influencing the decline in rate of severe perineal trauma.
| Variables | Adjusted R2 | R2 change (%) | F statistic | P value |
|---|---|---|---|---|
| Primary cesarean | 0.163 | 16.3 | 25.04 | <0.001 |
| Episiotomy | 0.648 | 48.7 | 178.34 | <0.001 |
| Forceps | 0.692 | 4.4 | 18.06 | <0.001 |
| Repeat cesarean | 0.703 | 1.1 | 5.39 | 0.022 |
| Total explained variance | 70.3 |
4. Discussion
This study examined which factors among the major validated antecedents of anal sphincter trauma (age, nulliparity, non–African American ethnicity, increased neonatal weight, use of forceps and vacuum extraction, and episiotomy, also described by other authors [2,4,10,12-15]) truly contribute to a reduction in the rate of severe perineal lacerations. Our findings have revealed that a reduction in the rates of the potentially modifiable validated risk factors, such as episiotomy and use of forceps, and the rise in the rate of primary cesarean delivery are, in fact, largely responsible for the reduction in the rate of severe perineal trauma over time.
The observed changes in the rates of severe perineal lacerations, episiotomy, forceps, and primary and repeat cesarean deliveries over the 11-year period at our center were found to be consistent with the national practice of obstetrics [4,18]. In the United States the overall rates for episiotomy have declined from 31% in 1997 [19] to less than 19% in 2001 [20], and rates for operative delivery have declined from 12.1% in 1989–1997 [21] to 3.5% in 2004 [20]. However, the overall rate of cesarean deliveries has risen from 20.7% in 1996 to over 30% in 2004 [22]. At our institution the change in the rate of operative deliveries consisted of a near-abandonment of the use of forceps from 7.6% in 1997 to 0.4% in 2006, which was accompanied by a low, almost unchanged, rate of vacuum extraction from 2.5% in 1996 to 2.8% in 2006 (Figure 1). On the other hand, the rate of episiotomy declined dramatically from 18.9% in 1996 to 3.1% in 2006, while the rate of primary cesarean deliveries rose from 12.4% in 1996 to 18.7% in 2006. These trends might explain why the contribution of the use of forceps to the overall decline in rate of severe perineal lacerations is significantly lower than that of episiotomy and primary cesarean deliveries. In fact, 70% of the four-fold reduction in anal sphincter trauma rate from 5.4% in 1996 to 1.3% in 2006 was primarily explained by a dramatic fall in the rate of episiotomy and a rise in primary cesarean delivery (Table 3).
Despite the obvious strengths, such as sample size and appropriate power to assess the presence of obstetrically-incurred anal sphincter trauma, the present study has several limitations. First, the study is based on the experience of a single center. Second, it is observational, rather than a trial, with attendant biases. Third, our analysis is limited to information previously collected. Therefore, because of their absence in our computerized perinatal database, position of fetal head (occiput anterior, occiput posterior) [23], length of second stage of labor [24], and body mass index—all potential predictors of severe perineal laceration—are not included in the current analysis. Furthermore, the proportion of women with severe perineal trauma who are asymptomatic cannot be identified. Finally, we were unable to evaluate and control for the training and expertise of the delivering attendants.
Despite these issues, the present study adds valuable information to the understanding of the major factors influencing the rates of severe perineal trauma. Given that most risk factors for anal sphincter lacerations (i.e. age, nulliparity, ethnicity, pelvic architecture, neonatal weight) are nonmodifiable, an obstetrician and a pregnant woman face difficult decisions regarding the risks and benefits of the modifiable interventions (i.e. episiotomy and operative vaginal delivery) when they are confronted with the need for expedited delivery in the second stage of labor or when spontaneous laceration is inevitable. In the authors' opinion, if episiotomy and/or operative delivery are indicated in women who are at a higher risk for severe perineal laceration (women who have never delivered vaginally, are older, of non–African American descent, who carry a large fetus, and desire to have 2 children [25]), after balancing the maternal and fetal risks of a vaginal delivery an obstetrician should first consider vacuum-assisted delivery rather than forceps, followed by episiotomy, possibly of the mediolateral type. There is some evidence which suggests that mediolateral episiotomy might not be as strongly associated with severe perineal trauma and genital prolapse [10]; it creates more perineal space for delivery rather than the midline technique, the most popular type of episiotomy used in the United States that frequently progresses to third- or fourth-degree perineal trauma. Finally, in some cases, an elective primary cesarean delivery might be desired. A study by Lowder et al. [2] supports the finding that primary cesarean deliveries contribute to the decline in severe perineal trauma. Their study demonstrated that women have a similar risk for severe perineal trauma after their first vaginal delivery (OR 5.1, 95% CI 4.4–5.9) and after vaginal birth after cesarean (OR 5.1, 95% CI 4.2–6.2), which suggests that severe perineal trauma can be avoided in women at risk who undergo cesarean delivery. However, a discussion regarding the indications for elective cesarean delivery is beyond the scope of this paper. Further studies are needed to evaluate an appropriate clinical decision-making process.
The findings of this study represent the results of an unintended, natural experiment at a tertiary teaching hospital (“surrogate” model) that reflect the major changes in the obstetric practice in the United States and changes in recommendations by the American College of Obstetricians and Gynecologists (ACOG) and the Agency for Healthcare Research and Quality practice. Our results show that reduction in rates of midline episiotomy, use of forceps, and rising cesarean delivery rates are major factors associated with the reduction in rates of perineal trauma. Thus, even though severe perineal trauma cannot be accurately predicted and the ideal rate of episiotomy for maximizing maternal and fetal well-being is unknown, time trends support a reduction in the rate of severe perineal trauma by restricting the liberal use of the 2 modifiable clinical variables: midline episiotomy and use of forceps.
Footnotes
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