Objective
The objective of the study was to evaluate the frequency of obstetrical anal sphincter injuries (OASIS) in women undergoing operative vaginal deliveries (OVD) and to assess whether a mediolateral episiotomy is protective for developing OASIS in these deliveries.
Study Design
We performed a retrospective cohort study. Maternal and obstetrical characteristics of the 2861 women who delivered liveborn infants by an OVD at term in the years 2001-2009 were extracted from a clinical obstetrics database and were analyzed in a logistic regression model.
Results
The frequency of OASIS was 5.7%. Women with a mediolateral episiotomy were at significantly lower risk for OASIS compared with the women without a mediolateral episiotomy in case of an OVD (adjusted odds ratio, 0.17; 95% confidence interval, 0.12–0.24).
Conclusion
We found a 6-fold decreased odds for developing OASIS when a mediolateral episiotomy was performed in OVD. Therefore, we advocate the use of a mediolateral episiotomy in all operative vaginal deliveries to reduce the incidence of OASIS.
Operative vaginal delivery is a risk factor for obstetrical anal sphincter injuries (OASIS). Other risk factors, identified by several studies, are primiparity, induction of labor, epidural anesthesia, occipitoposterior position, fetal macrosomia, increased maternal age, and prolonged duration of the second stage of labor. In The Netherlands in 2008, the frequency of OASIS defined as any rupture of the anal sphincter muscle was 2.3% in all vaginal deliveries.
To standardize the classification of perineal trauma, Sultan proposed a classification that has been adopted by the Royal College of Obstetricians and Gynaecologists (RCOG) with the injury being classified as minor (first and second degree) and major (third and fourth degree) according to the severity of injury. Knowledge of risk factors and preventive measures may help to reduce the number of anal sphincter injuries.
There is conflicting evidence in the literature about whether episiotomies may prevent OASIS. A metaanalysis of randomized trials and some earlier studies suggest that the risk of OASIS is increased with the use of a mediolateral episiotomy or was similar with no use of a mediolateral episiotomy. Most of these studies contained only a small number of deliveries and were therefore underpowered or did not use multivariate analysis. Other authors suggest that a mediolateral episiotomy could be protective for developing OASIS during operative vaginal delivery.
With this study, we hope to present more evidence that a mediolateral episiotomy lowers the odds for developing OASIS in the case of an operative vaginal delivery.
The aim of our study was to evaluate the frequency of OASIS in women undergoing an operative vaginal delivery and to assess whether a mediolateral episiotomy is protective for developing OASIS in these deliveries.
Materials and Methods
The Netherlands Perinatal Registry (PRN) is a national database that includes 96% of all approximately 190,000 deliveries per year at more than 16 completed weeks of gestation in The Netherlands, which are under supervision of a midwife or an obstetrician. After the delivery all the characteristics are recorded by the caregiver using a standardized electronic registration form. All the data are sent regularly to the national registry office, in which checks are conducted to validate the data. In the case of false records, the national registry office returns the data to the obstetrician to correct them. Previously the validity of the data entered into the PRN, such as perinatal mortality, is checked by comparing it with the Dutch civil registers. The conclusion of this study was that the quality of inputted data of the PRN was high.
A retrospective cohort study was performed using data from the (local) PRN database of the Amphia Hospital (Breda, The Netherlands) of deliveries from Jan. 1, 2001, through Dec. 31, 2009. According to Dutch law, the approval of the institutional review board was not needed because we used anonymous data from an existing clinical database of our hospital.
We selected all women who delivered liveborn infants by an operative vaginal delivery at term. All women with a multiple gestation or a breech delivery and delivered with a median episiotomy were excluded from the analysis.
We defined our primary outcome as OASIS. In our hospital, OASIS is diagnosed by the accoucheur. According to protocol the perineum is examined visually immediately after delivery with performance of a rectal examination. If the accoucheur was not a gynecologist (eg, a midwife or resident), the supervising obstetrician performed a second look to confirm the diagnosis of OASIS. According to the subdivision in the PRN database, perineal ruptures are categorized as none, rupture (first- and second-degree perineal rupture according to the RCOG classification), subtotal rupture (RCOG grade 3A, 3B, and 3C ruptures), and total rupture of the perineum (RCOG grade 4 rupture).
Continuous variables were compared using the Student t test or the nonparametric Mann-Whitney U test. The χ 2 test was used for categorical variables. Continuous variables were summarized as means with SDs or medians with interquartile ranges (IQRs). P < .05 was considered statistically significant.
A logistic regression model was used for the risk assessment of the use of a mediolateral episiotomy on the risk for developing OASIS. Treatment effect was presented as adjusted odds ratio (OR) with 95% confidence interval (CI). The number needed to treat (NNT) was calculated to assess the potential effectiveness of mediolateral episiotomy (MLE) by dividing 1 by the difference in OASIS probabilities between the MLE-positive and the MLE-negative group (eg, 1/(P MLE negative – P MLE positive ).
Results
The baseline characteristics of the 2 groups are shown in Table 1 . Patients in the group with a mediolateral MLE (MLE positive) delivered more frequently by a forceps extraction (12.7% vs 3.9%, P < .001), contained more occipitoposterior positions (13.2% vs 9.0%, P < .01), are more often primiparous (87.6% vs 73.5%, P < .001), and used epidural anesthesia more often (22.3% vs 13.8%, P < .001) compared with the group without a MLE (MLE negative). The MLE-negative group delivered more often by a vacuum extraction (96.1% vs 86.2%, P < .001) compared with the MLE-positive group.
| Characteristic | MLE+ a (n = 2316) | MLE− b (n = 545) | P value |
|---|---|---|---|
| Patient characteristics | |||
| Maternal age, y c | 34.6 ± 5.0 | 36.7 ± 5.1 | < .001 |
| Nationality e | |||
| Netherlands | 2085 (90.0%) | 485 (89.0%) | .206 |
| Mediterranean | 87 (3.8%) | 17 (3.1%) | .206 |
| Other European | 42 (1.8%) | 7 (1.3%) | .206 |
| Asian | 35 (1.5%) | 14 (2.6%) | .206 |
| African | 23 (1.0%) | 11 (2.0%) | .206 |
| Other | 39 (1.7%) | 9 (1.6%) | .206 |
| Unknown | 5 (0.2%) | 2 (0.4%) | .206 |
| Gestational age, d d | 282 (276–288) | 282 (276–288) | .243 |
| Primiparity e | 2026 (87.6%) | 399 (73.5%) | < .001 |
| Multiparity e | 288 (12.4%) | 144 (26.5%) | < .001 |
| Delivery characteristics | |||
| OASIS e | 77 (3.3%) | 85 (15.6%) | < .001 |
| Vacuum extraction e | 1996 (86.2%) | 524 (96.1%) | < .001 |
| Forceps extraction e | 295 (12.7%) | 21 (3.9%) | < .001 |
| Both vacuum and forceps extraction e | 25 (1.1%) | 0 (0%) | < .001 |
| Fetal distress is indication for OVD e | 769 (33.2%) | 180 (33.0%) | .960 |
| Occipitoanterior position e | 1914 (82.6%) | 481 (88.3%) | .006 |
| Occipitoposterior position e | 305 (13.2%) | 49 (9.0%) | .006 |
| Other cephalic positions e | 97 (4.2%) | 15 (2.7%) | .006 |
| Usage of epidural anesthesia e | 517 (22.3%) | 75 (13.8%) | < .001 |
| Duration second stage, min d | 79 (48.5–100) | 78 (53–98) | .352 |
| Blood loss, mL c | 519.7 ± 496.9 | 437.2 ± 365.5 | < .001 |
| Daytime obstetrics e | 1075 (46.4%) | 256 (47.0%) | .849 |
| Neonatal characteristics | |||
| Male e | 1275 (55.1%) | 312 (57.2%) | .363 |
| Birthweight, g c | 3519.4 ± 453.2 | 3530 ± 461.4 | .630 |
| Gestational age, d d | 282 (276–288) | 282 (276–288) | .243 |
| Apgar score after 1 minute d | 9 (8–9) | 8 (7–9) | < .001 |
| Apgar score after 5 minutes d | 10 (9–10) | 10 (9–10) | .057 |
| pH umbilical cord blood sampling c | 7.192 ± 0.853 | 7.189 ± 0.966 | .022 |
A total of 2861 operative vaginal deliveries in the study period were included in the analysis ( Figure ), and a total of 104 patients were excluded. The overall frequency of OASIS was 5.7%. In women delivered with a vacuum extraction, the frequency of sphincter lesions was 5.9% compared with 3.2% of women delivered with a forceps extraction.
The absolute risk of OASIS was respectively 3.5% in the MLE-positive group, compared with 15.6% in the MLE-negative group (OR, 0.19; 95% CI, 0.14–0.26). After the univariate logistic regression analysis, a multiple logistical model was used to account for the predefined covariates: gestational age at birth, parity, birthweight, maternal age, use of epidural analgesia, indication for operative vaginal delivery, cephalic fetal position, and duration of the second stage this risk estimation remained almost unchanged (adjusted OR, 0.17; 95% CI, 0.12–0.24).
The risk calculation for developing OASIS estimated for different covariates is shown in Table 2 . After the logistic regression analysis, controlling for different covariates, MLE showed a strong protective effect for developing OASIS with ORs varying from 0.13 up to 0.26. The protective effect of a mediolateral episiotomy was stronger in women delivered with a forceps extraction compared with women delivered with a vacuum extraction, as shown by the lower adjusted ORs in the group of women delivered with a forceps extraction.
| Variable | Vacuum extraction (n = 2520) | Forcipal extraction (n = 316) | ||||
|---|---|---|---|---|---|---|
| OASIS/n (%) | RR | Adjusted a OR (95% CI) | OASIS/n (%) | RR | Adjusted a OR (95% CI) | |
| Primiparity | ||||||
| MLE+ | 63/1750 (3.60) | 0.22 | 0.18 (0.12–0.26) | 3/254 (1.18) | 0.05 | 0.02 (0.00–0.17) |
| MLE− | 64/383 (16.71) | 1 | 4/16 (25) | 1 | ||
| Multiparity | ||||||
| MLE+ | 7/244 (2.87) | 0.29 | 0.26 (0.09–0.69) | 1/41 (2.44) | 0.06 | Not significant |
| MLE− | 14/139 (10.07) | 1 | 2/5 (40) | 1 | ||
| Occipitoanterior position | ||||||
| MLE+ | 53/1655 (3.20) | 0.22 | 0.18 (0.12–0.27) | 3/244 (1.23) | 0.04 | 0.02 (0.00–0.13) |
| MLE− | 69/464 (14.87) | 1 | 5/17 (29.4) | 1 | ||
| Occipitoposterior position | ||||||
| MLE+ | 16/260 (5.00) | 0.29 | 0.18 (0.06–0.51) | 1/35 (2.86) | 0.06 | Not significant |
| MLE− | 8/47 (17.02) | 1 | 1/2 (50) | 1 | ||
| Usage of epidural anesthesia | ||||||
| MLE+ | 17/466 (3.65) | 0.25 | 0.19 (0.08–0.44) | 1/48 (2.08) | 0.02 | Not significant |
| MLE− | 11/74 (14.86) | 1 | 1/1 (100) | 1 | ||
| Birthweight >4000 g | ||||||
| MLE+ | 15/289 (5.19) | 0.23 | 0.13 (0.06–0.32) | 1/40 (2.5) | 0.04 | Not significant |
| MLE− | 17/76 (22.37) | 1 | 3/5 (60) | 1 | ||
| Prolonged pushing (>60 min) | ||||||
| MLE+ | 58/1381 (4.20) | 0.24 | 0.20 (0.13–0.30) | 3/218 (1.38) | 0.03 | 0.02 (0.00–0.11) |
| MLE− | 59/339 (17.40) | 1 | 6/14 (42.86) | 1 | ||
| Total | ||||||
| MLE+ | 70/1996 (3.51) | 0.23 | 0.18 (0.13–0.26) | 4/295 (1.36) | 0.05 | 0.03 (0.00–0.14) |
| MLE− | 79/524 (15.08) | 1 | 6/21 (20.57) | 1 | ||
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