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Keywords:

  • Birth injuries;
  • delivery;
  • episiotomy;
  • perineum/injuries;
  • registries;
  • vacuum extraction

Abstract

  1. Top of page
  2. Abstract
  3. Introduction
  4. Methods
  5. Results
  6. Discussion
  7. Conclusions
  8. References
  9. Journal club
  10. Supporting Information

Please cite this paper as: Räisänen S, Vehviläinen-Julkunen K, Cartwright R, Gissler M, Heinonen S. Vacuum-assisted deliveries and the risk of obstetric anal sphincter injuries—a retrospective register-based study in Finland. BJOG 2012;119:1370–1378.

Objectives  To identify and quantify the risks of obstetric anal sphincter injury (OASIS) separately in nulliparae, including women admitted for a first vaginal delivery after a previous caesarean section for their first birth, and multiparae delivered by vacuum extraction in Finland where the type of episiotomy is exclusively lateral.

Design  A retrospective population-based register study.

Methods  Nulliparous and multiparous women with OASIS were compared separately with women without OASIS using stepwise logistic regression analysis.

Main outcome measures  Risk of OASIS.

Results  Among a sample of 16 802 women whose infants were delivered by vacuum extraction between 2004 and 2007, the incidence of OASIS was significantly higher among nulliparous women (475 of 13 981, 3.4%) than multiparous women (40 of 2821, 1.4%), with adjusted odds ratio 2.44 (95% CI 1.77–3.39). Lateral episiotomy was associated with 46% decreased incidence of OASIS (adjusted odds ratio 0.54, 95% CI 0.42–0.70) in nulliparae delivered by vacuum extraction. There was no statistically significant association for multiparous women. An increase of 1000 g in birthweight increased the OASIS incidence 2.10-fold for nulliparae and 2.83-fold for multiparae.

Conclusions  Nulliparous women with infants delivered by vacuum extraction had an increased risk of OASIS compared with multiparous women. Lateral episiotomy was associated with a decreased incidence of OASIS, especially in women with large babies and long second stage. These results support liberal use of lateral episiotomy at vacuum extraction for nulliparous women at high risk of OASIS, but the role of episiotomy should be re-investigated in interventional randomised trials.


Introduction

  1. Top of page
  2. Abstract
  3. Introduction
  4. Methods
  5. Results
  6. Discussion
  7. Conclusions
  8. References
  9. Journal club
  10. Supporting Information

Obstetric anal sphincter injury (OASIS) is a common complication of vaginal delivery, with the main risk factors including nulliparity, birthweight, operative vaginal deliveries1,2 and prolonged active second stage of birth.2 Results concerning perineum protection and the role of episiotomy performed either in midline, mediolateral or lateral positions have been conflicting. Mediolateral episiotomy is defined as an incision beginning in the midline, directed laterally and downwards away from the rectum, whereas lateral episiotomy begins in the vaginal introitus 1 or 2 cm lateral to the midline and is directed downwards towards the ischial tuberosity.3 Results of large population-based studies have been concordant, suggesting that both mediolateral and lateral episiotomies decrease the risk of OASIS in vaginal deliveries.1,4,5 However, there is limited evidence regarding the utility of episiotomy at operative vaginal delivery.

Forceps deliveries have been preferred in the USA, whereas vacuum extractions are favoured in Western Europe.6 Operative vaginal delivery remains a frequently used obstetric intervention, accounting for 6.5–8.4% of all deliveries in the Nordic countries and 11% in the UK in 2004.7 Vacuum assistance has been shown to increase the risk of OASIS by a factor of two to four in large population-based studies.1,2

Against this background little is understood of the risks associated with lateral episiotomy at vacuum-assisted deliveries, which is exclusively practiced in Finland,8 a country with a historically low OASIS incidence.9 We have previously found that delivering by vacuum extraction was one of the risk factors for OASIS and the use of lateral episiotomy was associated with a 30% decrease in incidence of OASIS in nulliparous women delivered by vacuum extraction in 1997–2007 in Finland.2 The present study was aimed to identify and quantify the risks for OASIS at vacuum-assisted deliveries separately for nulliparous women (n = 12 985), including women admitted for their first vaginal delivery after a previous caesarean section for their first birth (n = 996), and multiparous women (n = 2821) between 2004 and 2007. We selected that later period because the Finnish Medical Birth Register was updated in 2004 to include further relevant variables, and additionally the episiotomy rate was lower than 1997–2003, and more representative of current practice.

Methods

  1. Top of page
  2. Abstract
  3. Introduction
  4. Methods
  5. Results
  6. Discussion
  7. Conclusions
  8. References
  9. Journal club
  10. Supporting Information

The data were gathered from the Finnish Medical Birth Register, which includes information on maternal and neonatal birth characteristics and perinatal outcomes (all live births or stillbirths delivered after 22 weeks of gestation or weighing ≥500 g). The Medical Birth Register was established in 1987 and is currently compiled by the Finnish National Institute for Health and Welfare. Information on OASIS was collected from the Medical Birth Register and we also had information concerning all aspects of care during pregnancy and birth, such as diagnoses recorded using the International Classification of Diseases code and medical interventions and surgical procedures. The use of register data in scientific research required authorisation from the register keeper (the Finnish National Institute for Health and Welfare), as required by national data protection legislation. Only anonymised data were used and consequently the informed consent of the registered individuals was not needed.

The data included all singleton vacuum-assisted deliveries (n = 16 802), which comprised 8.9% of all vaginal deliveries (n = 189 834) between 2004 and 2007 in Finland. Nulliparous women (n = 12 985), women admitted for their first vaginal delivery after a previous caesarean section for their first birth (n = 996) and subsequent vaginal deliveries (n = 2821) were analysed separately because the risk of OASIS is known to be far greater in nulliparous women than in multiparous women.

The degree of OASIS was classified according to standard definitions: a third-degree rupture involves the external anal sphincter and a fourth-degree rupture affects both the anal sphincter and the anorectal mucosa.10 In all of the analyses, data on third-degree (89.8%) and fourth-degree (10.2%) obstetric anal sphincter ruptures were pooled to increase the power of the study. Active second stage of birth was defined as commencement of active pushing until delivery of the infant.

Statistical differences in frequencies (categorical and dichotomous variables) between the groups were evaluated by chi-square test. The differences between continuous variables were evaluated by Student’s t test and by Mann–Whitney U tests as appropriate. Multivariate logistic regression analyses were used to model the risk factors of OASIS among nulliparous women, nulliparous women including women admitted for first vaginal delivery after a previous caesarean section for their first birth and among multiparous women. Significant variables (P < 0.1) were selected based on univariate analyses. Among multiparous women, the risk of OASIS was also adjusted by parity modelled as a categorical variable. Of the multiparous women with OASIS (n = 40), 87.5% (n = 35) had had one previous vaginal delivery and so they were grouped into ‘one previous delivery’ or ‘two or more previous deliveries’. Continuous variables (birthweight and length of active second stage of birth) were used as covariates. Overall, the amount of missing information was minimal with the exception of 3364 women without information on length of active second stage of birth, which were excluded from the multivariate analyses. The data were analysed using spss for Windows 19.0 (SPSS Inc., Chicago, IL, USA).

Results

  1. Top of page
  2. Abstract
  3. Introduction
  4. Methods
  5. Results
  6. Discussion
  7. Conclusions
  8. References
  9. Journal club
  10. Supporting Information

Among both nulliparous women and women admitted for first vaginal delivery after a previous caesarean section for their first birth who were delivered by vacuum extraction the incidences of OASIS were significantly higher than in multiparous women (3.4 and 4.2% versus 1.4%, respectively, ≤ 0.001), at adjusted odds ratios (ORs) of 1.28 (95% CI 0.92–1.76) and 0.42 (95% CI 0.31–0.59). The incidences of OASIS among nulliparous and multiparous women with spontaneous deliveries were 1.3 and 0.2%, respectively (data not shown). There was a relatively higher prevalence of OASIS in women with infants weighing >4000 g among each group of women (Tables 1 and 2). Further, the mean length of the active second stage of birth was significantly longer among nulliparous and multiparous women with OASIS. Correspondingly, use of epidural analgesia was associated with a lower incidence of OASIS among each group of women but the results appeared to be significant only among the nulliparous women. Results on the use of episiotomy were more conflicting because among nulliparous women the use of the procedure was less frequent among women with OASIS; however, among both women admitted for first vaginal delivery after a previous caesarean section and multiparous women, episiotomy was associated with increased incidence of OASIS.

Table 1.   Delivery characteristics and interventions were compared between women delivered by vacuum extraction with and without OASIS within the groups of nulliparous (n = 12 985) and women admitted for first vaginal delivery after a previous caesarean section for their first birth (n = 996) between 2004 and 2007 in Finland
Delivery intervention/characteristicNulliparousFirst vaginal delivery after a previous caesarean section for their first birth
With OASIS (3.3%, =433)Without OASIS, P valueUnadjusted OR (95% CI)With OASIS (4.2%, =42)Without OASIS P valueUnadjusted OR (95% CI)
  1. Chi-square, Mann–Whitney U and Student’s t tests.

  2. *Data given as % or mean (±SD).

Gestational diabetes 1.42.20.070.41 (0.15–1.12)02.80.27
Mean maternal age (year)28.4 (±5.2)28.3 (±5.2)0.921.00 (0.99–1.02)32.0 (±3.8)31.5 (±4.7)0.431.03 (0.96–1.10)
Gestational age (weeks)
<370.52.70.010.18 (0.05–0.73)4.81.90.632.58 (0.57–11.67)
37–4056.963.2 164.365.6 1
41–4240.034.0 1.25 (1.02–1.52)31.032.4 1
≥4300.1 00.1 
Body mass index 23.4 (±4.1)23.6 (±4.4)0.300.99 (0.96–1.01)25.0 (±4.6)24.4 (±4.5)0.381.03 (0.96–1.10)
Mean length of active second stage of labour (minutes)83.8 (±67.3)65.5 (±56.0)≤0.001 55.7 (±39.5)59.5 (±54.6)0.60 
≤155.514.9≤0.00115.916.60.201
16–3016.819.32. 36 (1.38–4.04)26.523.63.16 (0.67–14.89)
31–4519.217.52.99 (1.76–5.07)29.416.35.08 (1.09–23.68)
46–6014.014.32.67 (1.54–4.62)11.814.72.26 (0.41–12.56)
>6044.534.03.47 (2.18–5.83)26.528.72.60 (0.55–12.77)
Mean birthweight (g)3690.2 (±414.6)3521.9 (±468.3)≤0.0012.19 (1.78–2.71) per 1 kg increase3686.6 (±554.6)3632.6 (±460.8)0.511.28 (0.66–2.49) per 1 kg increase
<30003.912.6≤0.001 11.97.70.38 
3000–349929.135.0 19.030.5 
3500–399945.037.3 42.937.7 
≥400021.915.2 26.222.1 
Induction 16.420.60.040.76 (0.59–0.98)38.119.30.0032.58 (1.35–4.90)
Augmentation with oxytocin 67.970.70.210.88 (0.72–1.08)66.764.70.791.09 (0.57–2.10)
Episiotomy 80.685.10.010.73 (0.57–0.93)73.883.00.120.58 (0.28–1.17)
Epidural analgesia 56.164.10.0010.72 (0.59–0.87)59.561.60.780.92 (0.49–1.72)
Nitrous oxide gas 52.455.50.200.88 (0.73–1.07)52.453.00.930.97 (0.53–1.80)
Paracervical block 12.212.90.670.94 (0.70–1.26)16.712.70.451.34 (0.60–3.10)
Table 2.   Delivery characteristics and interventions were compared between women delivered by vacuum extraction with and without OASIS in multiparous women (n = 2821) between 2004 and 2007 in Finland
Delivery intervention/characteristicMultiparous
With OASIS, (1.45, n = 40)Without OASIS P valueUnadjusted OR (95% CI)
  1. Chi-square, Mann–Whitney U and Student’s t tests.

Gestational diabetes 03.00.27
Mean maternal age (year)32.1 (±4.9)32.3 (±5.1)0.750.99 (0.93–1.05)
Gestational age (weeks)    
<370.01.70.85
37–4070.066.91
41–4230.031.30.92 (0.46–1.81)
≥430.00.1
Body mass index 25.0 (±4.8)24.6 (±4.7)0.571.02 (0.96–1.09)
Mean length of active second stage of labour (minutes)52.5 (±42.6)41.8 (±42.5)0.03 
≤1512.531.10.061
16–3021.923.62.31 (0.67–7.92)
31–4531.316.14.82 (1.51–15.47)
46–609.422.62.01 (0.45–9.06)
>6025.017.63.53 (1.06–11.80)
Mean birthweight (g)3932.03723.60.0092.40 (1.25–4.59)  per 1 kg increase
<30000.06.90.21 
3000–349922.524.0 
3500–399937.540.1 
≥400040.029.0 
Induction 12.523.00.120.48 (0.19–1.22)
Augmentation with oxytocin 50.064.00.070.56 (0.30–1.05)
Episiotomy 72.547.10.0012.96 (1.47–5.95)
Epidural analgesia 27.531.10.630.84 (0.42–1.69)
Nitrous oxide gas 57.553.90.651.16 (0.62–2.18)
Paracervical block 20.022.60.700.86 (0.39–1.87)

The results of univariate analyses were confirmed in multivariate analyses that showed that the difference in the incidence of OASIS among nulliparous women and those admitted for a first vaginal delivery after a previous caesarean section for their first birth remained insignificant (Table 3). Further, each additional increase of 1000 g in birthweight was associated with a 2.10-fold and 2.83-fold increase in incidence of OASIS for nulliparous women including women admitted for first vaginal delivery after a previous caesarean section for their first birth and multiparous women, respectively. In nulliparous women including women with a previous caesarean section, an increase of 1 hour in the second stage of labour was associated with a 19% increased incidence of OASIS (adjusted OR 1.19, 95% CI 1.08–1.32). In the same group, epidural analgesia and lateral episiotomy were associated with a decreased incidence of OASIS (adjusted OR 0.74, 95% CI 0.59–0.93 and adjusted OR 0.54, 95% CI 0.42–0.70, respectively) whereas among the multiparous women the association between use of episiotomy and incidence of OASIS did not reach statistical significance in multivariate analysis (adjusted OR 2.17, 95% CI 1.00–4.70). In multiparous women, the incidence of OASIS was associated with a 70% decrease in women who had had two or more previous deliveries compared with women with only one previous vaginal delivery (adjusted OR 0.30, 95% CI 0.10–0.89).

Table 3.   Adjusted odds ratio (OR) of OASIS* in nulliparous (n = 10 301), in nulliparous including women admitted for first vaginal delivery after a previous caesarean section for their first birth (n = 11 097) and multiparous women (n = 2337) women delivered by vacuum extraction between 2004 and 2007 in Finland
Delivery intervention/characteristicNulliparous OR (95% CI)Nulliparous/First vaginal delivery OR (95% CI)Multiparous OR (95% CI)
  1. OR of OASIS was adjusted by significant (P < 0.1) variables separately among each groups of women (See Tables 1 and 2).

  2. *OASIS rates among each groups of women were 328, 34 and 32, respectively.

  3. **Number of women with missing information on length of active second stage of birth was 2659 in nulliparous, 221 in women admitted for first vaginal delivery after a previous caesarean section for their first birth and 484 among multiparous women.

Nulliparous, first vaginal delivery 1
First vaginal delivery after caesarean section in first pregnancy  1.30 (0.90–1.87) 
Parity  
1 previous delivery  1
2+ previous deliveries  0.30 (0.10–0.89)
Gestational diabetes0.44 (0.16–1.20)0.38 (0.14–1.03)
Gestational age (weeks)  
<370.47 (0.11–1.93)0.60 (0.19–1.90) 
37–4011 
41–421.25 (0.99–1.58)1.19 (0.95–1.48) 
≥43 
Augmentation with oxytocin 0.43 (0.21–0.89)
Induction 0.70 (0.52–0.95)0.47 (0.16–1.36)
Epidural analgesia 0.73 (0.58–0.93)0.74 (0.59–0.93)
Length of active second stage of labour per 1-hour increase** 1.23 (1.11–1.36)1.19 (1.08–1.32)1.18 (0.76–1.84)
Episiotomy 0.56 (0.43–0.73)0.54 (0.42–0.70)2.17 (1.00–4.70)
Birthweight per 1000-g increase 2.17 (1.66–2.82)2.10 (1.64–2.69)2.83 (1.31–6.09)

Total episiotomy rate among both groups of women delivered by vacuum extraction was 78.5% whereas that among spontaneous vaginal deliveries over the study period was 24.8% (data not shown). In nulliparous women delivered by vacuum extraction, the incidence of OASIS was 4.3% in women without episiotomy and 3.2% in women with episiotomy (Table 4). In nulliparous women including women with a previous caesarean section who had an episiotomy and whose infants weighed >3500 g the OASIS rates were significantly lower (Table 5). Further, if the infant weighted >4000 g then the OASIS rate was 2.1-fold greater in women delivered without episiotomy compared with women delivered with episiotomy (8.8% versus 4.2%, P = 0.001). The differences between women who had episiotomy and who delivered without episiotomy are shown in Table 4, and the use of episiotomy in nulliparous women and in women with a previous caesarean section was clinically similar across birthweight groups and second-stage durations.

Table 4.   Delivery characteristics and interventions were compared between women delivered by vacuum extraction with and without episiotomy within the groups of nulliparous women, women with first vaginal delivery after caesarean in the first pregnancy, and multiparous women between 2004 and 2007 in Finland
Delivery intervention/characteristicNulliparous (n = 12 985)First vaginal delivery after a previous caesarean for the first birth (n = 996)Multiparous (n = 2780)
With episiotomy (84.9%)Without episiotomy P valueWith episiotomy (82.6%)Without episiotomy P valueWith episiotomy (47.9%)Without episiotomy P value
  1. Data are % or mean (±SD).

  2. Chi-square, Mann–Whitney U and Student’s t tests).

OASIS 3.24.30.013.86.40.122.20.80.002
Gestational diabetes 2.12.50.292.82.30.72330.94
Mean maternal age (year)28.3 (±5.2)28.5 (±5.2)0.1831.5 (±4.6)31.7 (±5.0)0.4931.9 (±5.0)32.8 (±5.1)≤0.001
Gestational age (weeks)
<372.53.40.11.25.8≤0.0011.51.90.03
37–4063.262.564.272.264.668.9
41–4234.333.934.52233.929.1
≥430.10.10.1000.1
Mean length of active second stage of birth (minutes)65.6 (±55.9)68.3 (±59.4)0.1858.1 (±52.9)65.2 (±58.2)0.00544.4 (±43.1)39.9 (±42.0)≤0.001
≤1514.515.50.3516.514.60.5725.335.7≤0.001
16–3019.318.823.823.625.322
31–4517.716.817.713.218.314.5
46–6014.513.214.116.712.810.4
>6034.135.727.931.918.217.3
Mean birthweight (g)3538.4 (±463.0)3466.4 (±488.6)≤0.0013654.3 (±455.2)3548.2 (±500.0)0.273750.0 (±485.2)3714.2 (±509.2)0.04
<300011.616.1≤0.0016.812.70.015.97.20.18
3000–349934.735.32934.72424.1
3500–399937.935.640.934.73940.9
>400015.81323.217.931.127.9
Induction 20.321.30.2720.219.70.8822.823.40.69
Augmentation with oxytocin 65.171.6≤0.00166.158.40.0568.560.7≤0.001
Epidural analgesia 63.267.4≤0.00160.964.70.3434.428.1≤0.001
Nitrous oxide gas 56.350.5≤0.0015353.20.9657.451.50.001
Paracervical block 13.211.10.0091312.10.7620.525.10.004
Table 5.   Incidence of OASIS in nulliparous women including women admitted for first vaginal delivery after caesarean for first birth delivered by vacuum extraction with and without episiotomy (n = 13 981) between 2004 and 2007 in Finland
Delivery intervention/characteristicOASIS %
With episiotomyWithout episiotomy P value
  1. *Among nulliparous women who had information on length of active second stage of birth.

Vacuum extraction 3.24.50.003
Vacuum extraction* 2.95.1≤0.001
Length of active second stage of birth (minutes)
≤602.64.20.003
≥613.66.7≤0.001
Birthweight (g)
<30001.31.50.76
3000–34992.82.90.79
3500–39993.85.70.01
≥40004.28.80.001

Discussion

  1. Top of page
  2. Abstract
  3. Introduction
  4. Methods
  5. Results
  6. Discussion
  7. Conclusions
  8. References
  9. Journal club
  10. Supporting Information

The aim of the present study was to identify and quantify the risks for OASIS at vacuum-assisted delivery separately for nulliparous women, women admitted for a first vaginal delivery after a previous caesarean section for their first birth, and multiparous women. The data included all vacuum-assisted deliveries for the years 2004–07, comprising 8.9% of all vaginal deliveries over the period. The occurrence of OASIS was significantly higher in nulliparous women and in women admitted for a first vaginal delivery after a previous caesarean section for their first birth than in multiparous women (3.3%, 4.2% versus 1.4%, respectively) and furthermore, two or more previous deliveries among the multiparous women were associated with a 70% decreased incidence of OASIS compared with women with only one previous vaginal delivery. The difference in the incidence of OASIS between nulliparous women and women with a previous caesarean section for their first birth appeared to be insignificant after adjustment. Interestingly, the use of lateral episiotomy was associated with a 46% lower incidence of OASIS (adjusted OR 0.54, 95% CI 0.42–0.70) in nulliparous women including women with a first vaginal delivery after a previous caesarean section who were delivered by vacuum extraction, whereas in multiparous women the association was statistically insignificant. Increasing birthweight by 1000 g was associated with a more than two-fold increase in incidence of OASIS among each group of women. Furthermore, in nulliparous women including women with a previous caesarean section who were delivered by vacuum extraction the OASIS was associated with increased incidence by the length of the second stage.

The most important strength of our analysis was that the data covered all the women in Finland delivered by vacuum extraction over a 4-year period. The data were derived from the mandatory, national, population-based Medical Birth Register, which has been shown to have excellent coverage and to contain good-quality data.9,11 The analysis therefore offers a comprehensive and generalisable picture of OASIS risks separately for nulliparous and multiparous women. A possible weakness is the potential for differential misclassification bias, plausibly affecting risk factors including parity and episiotomy. Further, there might have been systematic differences in registration routines and recognition of OASIS between hospitals. However, the strength was that we had information concerning all aspects of care during pregnancy and birth, such as International Classification of Diseases codes, medical interventions and surgical procedures.

The risk factors of OASIS in vacuum-assisted deliveries included high birthweight and prolonged second stage of labour in nulliparous women including women admitted for a first vaginal delivery after a previous caesarean section for their first birth. Among all groups of women the use of epidural analgesia was associated with a decreased incidence of OASIS but the results appeared to be significant only in nulliparous women excluding women with a previous caesarean section. These results might be explained by the fact that women were more relaxed. However, previous data are inconsistent regarding the use of epidural analgesia, which has been associated with both increased and reduced risks of OASIS; although these studies included spontaneous vaginal deliveries.12–14

Use of lateral episiotomy was associated with a decreased incidence of OASIS in nulliparous women and women with a previous caesarean section for their first birth but not in multiparous women. The results of the present study were in line with our previous results concerning the risk factors of OASIS among singleton vaginal deliveries but among the nulliparous women delivered by vacuum extraction the use of lateral episiotomy was associated with c.50% decreased incidence of OASIS compared with nulliparous women delivered by vacuum extraction without episiotomy.2 Our results were in line with those of a previous study concerning risk factors of OASIS in operative vaginal deliveries.15 It should be noted, however, that in that study the episiotomy type used was mediolateral, and nulliparous and multiparous women were pooled in the analyses. The results of that study also demonstrated that birthweight and the duration of second stage of birth were associated with increased incidence of OASIS in vacuum-assisted deliveries, whereas mediolateral episiotomy decreased the OASIS risk by 89%. The positive effect of episiotomy in preventing OASIS in their study could be explained by a higher overall rate of OASIS, or a true difference between episiotomy techniques. Furthermore, the results of another large retrospective study (n = 1 673 442) were also in line with the present results, demonstrating that mediolateral episiotomy decreased the OASIS risk by 20% in primiparous women delivered by vacuum extraction (n = 20 980).1 In that study, OASIS rates in vacuum-assisted deliveries with and without episiotomy were much higher: 13.8 and 15.6%. Overall, large population-based studies appear to be coherent and suggest that lateral and mediolateral episiotomy techniques have been associated with a decreased incidence of OASIS in vacuum-assisted deliveries. The results of subgroup analyses in our study suggested that lateral episiotomy was associated with a decreased incidence of OASIS especially in nulliparous women with larger infants and in the case of a prolonged active second stage of birth.

Only 40 multiparous women delivered by vacuum extraction (1.4%) were affected by OASIS. Univariate analysis demonstrated a significant difference in OASIS rates between women delivered with and without episiotomy but the increase of incidence caused by episiotomy attenuated in multivariate analysis, where only parity, augmentation with oxytocin, induction and birthweight remained significant. This may be explained by a type II error because of the low number of cases. Further, it might be that episiotomy was performed prophylactically more often in those who were at a high risk of OASIS than in low-risk women, consequently there might have been confounding by indication. Based on the results of the present study we conclude that the role of episiotomy in vacuum-assisted deliveries should be re-investigated in interventional randomised trials, for both groups of women.

The results of the present study are applicable to countries with a similar risk profile of OASIS but may be very different in countries with markedly lower or higher OASIS rates. In particular, non-use of forceps, and use of lateral episiotomy may reduce generalisability.

Conclusions

  1. Top of page
  2. Abstract
  3. Introduction
  4. Methods
  5. Results
  6. Discussion
  7. Conclusions
  8. References
  9. Journal club
  10. Supporting Information

The results of the present study on women delivered by vacuum extraction provide evidence that OASIS risk incrementally decreases with each vaginal delivery. Birthweight and the length of the second stage have a dose-dependent positive association with OASIS, whereas lateral episiotomy was associated with a c.50% decreased incidence of OASIS in nulliparous women including women admitted for a first vaginal delivery after a previous caesarean section for their first birth. Among nulliparous women, the procedure was associated with a decreased incidence, especially with large infants and in women with prolonged active second stage of birth. Further, because of the observational study design we were able to reveal only associations between the role of episiotomy and OASIS, and therefore the role of mediolateral and lateral episiotomy techniques in vacuum-assisted deliveries should be re-investigated in interventional randomised trials, for both groups of women.

Disclosure of interests

None declared. All authors declare, as researchers, independence from the funders.

Contribution of authorship

SR, KV-J, MG and SH participated in designing the study. SR managed the dataset and performed statistical analyses. KV-J, RC, MG and SH gave advice regarding the statistical analyses. All authors contributed to the interpretation of the results, as well as to the writing and editing of the manuscript.

Details of ethical approval

The permission to use the confidential register data in this study was approved on 16 October 2008 by the National Institute for Health and Welfare in Finland (reference number 2777/605/2007).

Funding

No funding was received for this study.

References

  1. Top of page
  2. Abstract
  3. Introduction
  4. Methods
  5. Results
  6. Discussion
  7. Conclusions
  8. References
  9. Journal club
  10. Supporting Information

Journal club

  1. Top of page
  2. Abstract
  3. Introduction
  4. Methods
  5. Results
  6. Discussion
  7. Conclusions
  8. References
  9. Journal club
  10. Supporting Information

Discussion points

  • 1
     Background: Compare the incidence in your hospital or country with the incidence in this study.
    Describe the difference between lateral and mediolateral episiotomy.1
  • 2
     Methods: Summarise the benefits and pitfalls of using a population-based birth register for research studies.
    Birthweight can be estimated before a ventouse delivery, but can only be accurately confirmed postpartum. Debate its use as a predictive factor for this study.
    Women with a previous caesarean were examined as one group and considered similar to nulliparous women in this study. Some of these women might have had a failed trial of assisted vaginal delivery leading to their caesarean birth. Discuss.
  • 3
     Results and implications: Discuss the number of episiotomies needed to prevent (number-needed-to-treat) one obstetric anal sphincter injury (OASIS).
    This paper treats OASIS as one outcome, whereas the extent of injury to the anal structures has been shown to be important for long-term outcomes.2 Discuss the implications.
    Compare the conclusions of this paper with other papers and current guidelines for operative delivery.3,4 Can these findings be translated to countries where the practice of episiotomy is mediolateral as opposed to lateral? Would this paper affect your counselling of women when consenting for operative vaginal delivery? (Data S1)

D Siassakos & R Simms

School of Clinical Sciences, Southmead Hospital, University of Bristol, Bristol, UK Email jsiasakos@gmail.com

Further reading

  1. Top of page
  2. Abstract
  3. Introduction
  4. Methods
  5. Results
  6. Discussion
  7. Conclusions
  8. References
  9. Journal club
  10. Supporting Information

Supporting Information

  1. Top of page
  2. Abstract
  3. Introduction
  4. Methods
  5. Results
  6. Discussion
  7. Conclusions
  8. References
  9. Journal club
  10. Supporting Information

Data S1. Powerpoint slides summarising the study.

FilenameFormatSizeDescription
BJO_3455_sm_DataS1.pptx336KSupporting info item

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