ofi

Meeting Papers www.AJOG.orgFast-Track papers from the 2012 meeting of the Society for Maternal–Fetal Medicine

The effect of a mediolateral episiotomy during operativevaginal delivery on the risk of developingobstetrical anal sphincter injuriesJoey de Vogel, MD; Anneke van der Leeuw-van Beek, MD; Dirk Gietelink, MD, PhD; Marijana Vujkovic, PhD;Jan Willem de Leeuw, MD, PhD; Jeroen van Bavel, MD; Dimitri Papatsonis, MD, PhD

OBJECTIVE: The objective of the study was to evaluate the frequency ofobstetrical anal sphincter injuries (OASIS) in women undergoing opera-tive vaginal deliveries (OVD) and to assess whether a mediolateral epi-siotomy is protective for developing OASIS in these deliveries.

STUDY DESIGN: We performed a retrospective cohort study. Maternal andbstetrical characteristics of the 2861 women who delivered liveborn in-ants by an OVD at term in the years 2001-2009 were extracted from a clin-cal obstetrics database and were analyzed in a logistic regression model.

RESULTS: The frequency of OASIS was 5.7%. Women with a mediolat-

eral episiotomy were at significantly lower risk for OASIS compared with

of developing obstetrical anal sphincter injuries. Am J Obstet Gynecol 2012;206:404

tl(m(v

mediolateral episiotomdoi: 10.1016/j.ajog.2012.02.008

404.e1 American Journal of Obstetrics & Gynecology MAY 2012

the women without a mediolateral episiotomy in case of an OVD (ad-justed odds ratio, 0.17; 95% confidence interval, 0.12–0.24).

CONCLUSION: We found a 6-fold decreased odds for developing OASISwhen a mediolateral episiotomy was performed in OVD. Therefore, weadvocate the use of a mediolateral episiotomy in all operative vaginaldeliveries to reduce the incidence of OASIS.

Key words: mediolateral episiotomy, obstetrical anal sphincter

injuries, operative vaginal delivery

Cite this article as: de Vogel J, van der Leeuw-van Beek A, Gietelink D, et al. The effect of a mediolateral episiotomy during operative vaginal delivery on the risk

.e1-5.

aifnac

Operative vaginal delivery is a riskfactor for obstetrical anal sphinc-

ter injuries (OASIS). Other risk factors,identified by several studies, are primi-parity, induction of labor, epidural anes-thesia, occipitoposterior position, fetal

From the Departments of Obstetrics andGynaecology, Amphia Hospital Breda, Breda(Drs de Vogel, van der Leeuw-van Beek,Gietelink, van Bavel, and Papatsonis); ErasmusMedical Center, Rotterdam (Dr Vujkovic); andIkazia Hospital Rotterdam, Rotterdam (Dr deLeeuw), The Netherlands.

Received Nov. 27, 2011; revised Jan. 26,2012; accepted Feb. 13, 2012.

The authors report no conflict of interest.

Presented at the 32nd annual meeting of theSociety for Maternal-Fetal Medicine, Dallas, TX,Feb. 6-11, 2012.

The racing flag logo above indicates that thisarticle was rushed to press for the benefit of thescientific community.

Reprints: Joey de Vogel, MD, Department ofObstetrics and Gynaecology, Amphia HospitalBreda, Langendijk 75, 4819 EV, Breda, TheNetherlands. joeydevogel@gmail.com.

0002-9378/$36.00© 2012 Mosby, Inc. All rights reserved.

macrosomia, increased maternal age, andprolonged duration of the second stage oflabor.1-5 In The Netherlands in 2008, thefrequency of OASIS defined as any ruptureof the anal sphincter muscle was 2.3% in allvaginal deliveries.6

To standardize the classification of peri-neal trauma, Sultan7 proposed a classifica-ion that has been adopted by the Royal Col-ege of Obstetricians and GynaecologistsRCOG) with the injury being classified asinor (first and second degree) and major

thirdandfourthdegree)accordingtothese-erity of injury.8 Knowledge of risk factors

and preventive measures may help to reducethe number of anal sphincter injuries.

There is conflicting evidence in the lit-erature about whether episiotomies mayprevent OASIS.9 A metaanalysis of ran-domized trials and some earlier studiessuggest that the risk of OASIS is in-creased with the use of a mediolateralepisiotomy or was similar with no use ofa mediolateral episiotomy.10-15 Most ofthese studies contained only a smallnumber of deliveries and were thereforeunderpowered or did not use multivari-ate analysis. Other authors suggest that a

y could be pro- o

tective for developing OASIS during op-erative vaginal delivery.16,17

With this study, we hope to presentmore evidence that a mediolateral episiot-omy lowers the odds for developing OASISin the case of an operative vaginal delivery.

The aim of our study was to evaluatethe frequency of OASIS in women un-dergoing an operative vaginal deliveryand to assess whether a mediolateralepisiotomy is protective for developingOASIS in these deliveries.

MATERIALS AND METHODSThe Netherlands Perinatal Registry (PRN)is a national database that includes 96% ofall approximately 190,000 deliveries peryear at more than 16 completed weeks ofgestation in The Netherlands, which areunder supervision of a midwife or an ob-stetrician. 6 After the delivery all the char-cteristics are recorded by the caregiver us-ng a standardized electronic registrationorm. All the data are sent regularly to theational registry office, in which checksre conducted to validate the data. In thease of false records, the national registry

ffice returns the data to the obstetrician to

s

tliafitpseMg

ery,

www.AJOG.org SMFM Papers

correct them. Previously the validity of thedata entered into the PRN, such as perina-tal mortality, is checked by comparing itwith the Dutch civil registers. The conclu-sion of this study was that the quality of

TABLE 1General characteristics

CharacteristicM(n

Patient characteristics..........................................................................................................

Maternal age, yc

..........................................................................................................

Nationalitye

.................................................................................................

Netherlands 20.................................................................................................

Mediterranean.................................................................................................

Other European.................................................................................................

Asian.................................................................................................

African.................................................................................................

Other.................................................................................................

Unknown..........................................................................................................

Gestational age, dd 2..........................................................................................................

Primiparitye 20..........................................................................................................

Multiparitye 2...................................................................................................................

Delivery characteristics..........................................................................................................

OASISe

..........................................................................................................

Vacuum extractione 19..........................................................................................................

Forceps extractione 2..........................................................................................................

Both vacuum and forceps extractione

..........................................................................................................

Fetal distress is indication for OVDe 7..........................................................................................................

Occipitoanterior positione 19..........................................................................................................

Occipitoposterior positione 3..........................................................................................................

Other cephalic positionse

..........................................................................................................

Usage of epidural anesthesiae 5..........................................................................................................

Duration second stage, mind

..........................................................................................................

Blood loss, mLc 5..........................................................................................................

Daytime obstetricse 10...................................................................................................................

Neonatal characteristics..........................................................................................................

Malee 12..........................................................................................................

Birthweight, gc 35..........................................................................................................

Gestational age, dd 2..........................................................................................................

Apgar score after 1 minuted

..........................................................................................................

Apgar score after 5 minutesd

..........................................................................................................

pH umbilical cord blood samplingc

...................................................................................................................

Data on blood loss was missing in 11 MLE� and 53 MLE� pin 312 MLE� and 968 MLE� patients. The characteristics weMLE�).MLE, mediolateral episiotomy.a With an MLE; b Without an MLE; c Mean � SD; d Median (p

de Vogel. Mediolateral episiotomy, operative vaginal deliv

inputted data of the PRN was high.18

A retrospective cohort study was per-formed using data from the (local) PRNdatabase of the Amphia Hospital (Breda,The Netherlands) of deliveries from Jan.1, 2001, through Dec. 31, 2009. Accord-

a

2316)MLE�b

(n � 545) P value

..................................................................................................................

6 � 5.0 36.7 � 5.1 � .001..................................................................................................................

..................................................................................................................

(90.0%) 485 (89.0%) .206..................................................................................................................

(3.8%) 17 (3.1%) .206..................................................................................................................

(1.8%) 7 (1.3%) .206..................................................................................................................

(1.5%) 14 (2.6%) .206..................................................................................................................

(1.0%) 11 (2.0%) .206..................................................................................................................

(1.7%) 9 (1.6%) .206..................................................................................................................

(0.2%) 2 (0.4%) .206..................................................................................................................

(276–288) 282 (276–288) .243..................................................................................................................

(87.6%) 399 (73.5%) � .001..................................................................................................................

(12.4%) 144 (26.5%) � .001..................................................................................................................

..................................................................................................................

(3.3%) 85 (15.6%) � .001..................................................................................................................

(86.2%) 524 (96.1%) � .001..................................................................................................................

(12.7%) 21 (3.9%) � .001..................................................................................................................

(1.1%) 0 (0%) � .001..................................................................................................................

(33.2%) 180 (33.0%) .960..................................................................................................................

(82.6%) 481 (88.3%) .006..................................................................................................................

(13.2%) 49 (9.0%) .006..................................................................................................................

(4.2%) 15 (2.7%) .006..................................................................................................................

(22.3%) 75 (13.8%) � .001..................................................................................................................

(48.5–100) 78 (53–98) .352..................................................................................................................

7 � 496.9 437.2 � 365.5 � .001..................................................................................................................

(46.4%) 256 (47.0%) .849..................................................................................................................

..................................................................................................................

(55.1%) 312 (57.2%) .363..................................................................................................................

4 � 453.2 3530 � 461.4 .630..................................................................................................................

(276–288) 282 (276–288) .243..................................................................................................................

(8–9) 8 (7–9) � .001..................................................................................................................

(9–10) 10 (9–10) .057..................................................................................................................

192 � 0.853 7.189 � 0.966 .022..................................................................................................................

ts. Data on pH umbilical cord blood sampling was missingouped by the use of a mediolateral episiotomy (MLE� and

75); e n (%).

and OASIS. Am J Obstet Gynecol 2012.

ing to Dutch law, the approval of the in-

MAY 2012 Americ

stitutional review board was not neededbecause we used anonymous data froman existing clinical database of ourhospital.

We selected all women who deliveredliveborn infants by an operative vaginaldelivery at term. All women with a mul-tiple gestation or a breech delivery anddelivered with a median episiotomy wereexcluded from the analysis.

We defined our primary outcome asOASIS. In our hospital, OASIS is diag-nosed by the accoucheur. According toprotocol the perineum is examined visu-ally immediately after delivery with perfor-mance of a rectal examination. If the ac-coucheur was not a gynecologist (eg, amidwife or resident), the supervising ob-stetrician performed a second look to con-firm the diagnosis of OASIS. According tothe subdivision in the PRN database, peri-neal ruptures are categorized as none, rup-ture (first- and second-degree perinealrupture according to the RCOG classifica-tion), subtotal rupture (RCOG grade 3A,3B, and 3C ruptures), and total rupture ofthe perineum (RCOG grade 4 rupture).8

Continuous variables were comparedusing the Student t test or the nonpara-metric Mann-Whitney U test. The �2 testwas used for categorical variables. Con-tinuous variables were summarized asmeans with SDs or medians with inter-quartile ranges (IQRs). P � .05 was con-idered statistically significant.

A logistic regression model was used forhe risk assessment of the use of a medio-ateral episiotomy on the risk for develop-ng OASIS. Treatment effect was presenteds adjusted odds ratio (OR) with 95% con-dence interval (CI). The number needed

o treat (NNT) was calculated to assess theotential effectiveness of mediolateral epi-iotomy (MLE) by dividing 1 by the differ-nce in OASIS probabilities between the

LE-positive and the MLE-negativeroup (eg, 1/(PMLE negative – PMLE positive).

RESULTSThe baseline characteristics of the 2 groupsare shown in Table 1. Patients in the groupwith a mediolateral MLE (MLE positive)delivered more frequently by a forceps ex-traction (12.7% vs 3.9%, P � .001), con-

LE��

.........

34..........

.........

85.........

87.........

42.........

35.........

23.........

39.........

5.........

82.........

26.........

88.........

.........

77.........

96.........

95.........

25.........

69.........

14.........

05.........

97.........

17.........

79.........

19..........

75.........

.........

75.........

19..........

82.........

9.........

10.........

7..........

atienre gr

25–p

tained more occipitoposterior positions

an Journal of Obstetrics & Gynecology 404.e2

pa(wamvM

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SMFM Papers www.AJOG.org

(13.2% vs 9.0%, P � .01), are more oftenrimiparous (87.6% vs 73.5%, P � .001),nd used epidural anesthesia more often22.3% vs 13.8%, P � .001) comparedith the group without a MLE (MLE neg-

tive). The MLE-negative group deliveredore often by a vacuum extraction (96.1%

s 86.2%, P � .001) compared with theLE-positive group.A total of 2861 operative vaginal deliv-

ries in the study period were included inhe analysis (Figure), and a total of 104atients were excluded. The overall fre-uency of OASIS was 5.7%. In womenelivered with a vacuum extraction, the

requency of sphincter lesions was 5.9%ompared with 3.2% of women deliv-red with a forceps extraction.

The absolute risk of OASIS was respec-ively 3.5% in the MLE-positive group, com-ared with 15.6% in the MLE-negativeroup (OR, 0.19; 95% CI, 0.14 – 0.26).fter the univariate logistic regressionnalysis, a multiple logistical model wassed to account for the predefined cova-iates: gestational age at birth, parity,irthweight, maternal age, use of epidu-al analgesia, indication for operativeaginal delivery, cephalic fetal position,nd duration of the second stage this riskstimation remained almost unchangedadjusted OR, 0.17; 95% CI, 0.12– 0.24).

The risk calculation for developingASIS estimated for different covariates

s shown in Table 2. After the logistic re-ression analysis, controlling for differ-nt covariates, MLE showed a strongrotective effect for developing OASISith ORs varying from 0.13 up to 0.26.he protective effect of a mediolateralpisiotomy was stronger in women de-ivered with a forceps extraction com-ared with women delivered with a vac-um extraction, as shown by the lowerdjusted ORs in the group of women de-ivered with a forceps extraction.

The NNT for the use of a mediolateralpisiotomy during vacuum extraction torevent 1 anal sphincter injury was 8.64,hereas the NNT in a forceps deliveryas 5.21. These NNT values are relatively

ow compared with, for example, 63 forhe treatment with magnesium sulphate

n severe preeclampsia.19

404.e3 American Journal of Obstetrics & Gynecolo

COMMENT

We analyzed the decreased odds for de-veloping OASIS, associated with the useof a mediolateral episiotomy, in 2861 pa-tients delivered by an operative vaginaldelivery.

When a mediolateral episiotomy was per-formed, the odds for developing OASISdeceased 6-fold.

Our practice is part of one of the larg-est general teaching hospitals in TheNetherlands with more than 3000 deliv-eries per annum. In our departmentwomen are allowed to deliver after 32weeks’ gestational age. As is common inThe Netherlands, the use of vacuum ex-traction is more common in operativevaginal deliveries (OVDs). Only a fewtrained gynecologists handle the forcepsand only in the case of an outlet forcepsand occipitoposterior position. There-fore, the number of 321 forceps deliver-ies in contrast to the 2520 vacuum deliv-eries is a reflection of Dutch obstetricalpractice. Because of the low number offorceps deliveries in our study, the calcu-lated protective effect and NNT have to

FIGUREFlow diagram of the included patie

he flow diagram of the included patients was divLE, mediolateral episiotomy.

e Vogel. Mediolateral episiotomy, operative vaginal delivery

be interpreted with caution.

gy MAY 2012

Known risk factors for developingOASIS (eg, primiparity, occipitoposte-rior position, and forceps delivery) areoverrepresented in the MLE-positivegroup, compared with the MLE-negativegroup. Despite this inequality, the fre-quency of OASIS is lower in the MLE-positive group, which may indicate thatthe reducing effect of a mediolateral epi-siotomy on the risk for developing OA-SIS is even underestimated.

In our study the use of a mediolateralepisiotomy has a strong protective ef-fect on the occurrence of anal sphinc-ter laceration during an operative vag-inal delivery, with a 6-fold decreasedodds for developing OASIS. Our re-sults are corroborated by the results ofprevious studies on this subject.17,20

Combs et al20 also showed that medio-lateral episiotomy was protective againstanal sphincter damage after an opera-tive vaginal delivery. de Leeuw et al17

demonstrated that a mediolateral epi-siotomy protected significantly foranal sphincter damage in both vacuumextraction and forceps delivery. In thatstudy the number of mediolateral epi-

into 2 groups (MLE positive and MLE negative).

OASIS. Am J Obstet Gynecol 2012.

nts

T idedM

d , and

siotomies needed to prevent 1 sphinc-

ery,

www.AJOG.org SMFM Papers

ter injury in vacuum extractions was12, whereas 5 mediolateral episioto-mies could prevent 1 sphincter injuryin forceps deliveries.17

The strength of this study is the largenumber of analyzed deliveries collectedin a prospective manner. The weaknessesof this study are the retrospective studydesign, the inequality at baseline be-tween the 2 groups (although the differ-ences are minimized by using a logisticregression model), and no standardiza-tion of how and when a MLE was per-formed. Also, the database is lacking the

TABLE 2Multivariate analysis on the risk fo

Variable

Vacu

OASI

Primiparity..........................................................................................................

MLE� 63/17..........................................................................................................

MLE� 64/38...................................................................................................................

Multiparity..........................................................................................................

MLE� 7/24..........................................................................................................

MLE� 14/13...................................................................................................................

Occipitoanterior position..........................................................................................................

MLE� 53/16..........................................................................................................

MLE� 69/46...................................................................................................................

Occipitoposterior position..........................................................................................................

MLE� 16/26..........................................................................................................

MLE� 8/47...................................................................................................................

Usage of epidural anesthesia..........................................................................................................

MLE� 17/46..........................................................................................................

MLE� 11/74...................................................................................................................

Birthweight �4000 g..........................................................................................................

MLE� 15/28..........................................................................................................

MLE� 17/76...................................................................................................................

Prolonged pushing (�60 min)..........................................................................................................

MLE� 58/13..........................................................................................................

MLE� 59/33...................................................................................................................

Total..........................................................................................................

MLE� 70/19..........................................................................................................

MLE� 79/52...................................................................................................................

CI, confidence interval; MLE, mediolateral episiotomy; OASIS,a Adjusted for: maternal age, parity, presence of fetal distress

de Vogel. Mediolateral episiotomy, operative vaginal deliv

registration of adverse effects of the use

of a MLE, which makes it impossible totake these possible effects into account.Despite the weaknesses of this study, theevident and considerable protective ef-fect of the MLE clearly is of clinicalimportance.

Although adverse effects are not re-ported in our study, the known adverseeffects of the mediolateral episiotomy(eg, short-term healing pain, dyspareu-nia, etc) are, in our opinion, causing lessmorbidity compared with the known ad-verse effects of OASIS (eg, fecal inconti-nence). Therefore, the significant risk

eveloping OASIS in vacuum deliverie

extraction (n � 2520)

(%) RRAdjusteda OR(95% CI)

.........................................................................................................................

(3.60) 0.22 0.18 (0.12–0.26).........................................................................................................................

6.71) 1.........................................................................................................................

.........................................................................................................................

.87) 0.29 0.26 (0.09–0.69).........................................................................................................................

0.07) 1.........................................................................................................................

.........................................................................................................................

(3.20) 0.22 0.18 (0.12–0.27).........................................................................................................................

4.87) 1.........................................................................................................................

.........................................................................................................................

.00) 0.29 0.18 (0.06–0.51).........................................................................................................................

.02) 1.........................................................................................................................

.........................................................................................................................

.65) 0.25 0.19 (0.08–0.44).........................................................................................................................

.86) 1.........................................................................................................................

.........................................................................................................................

.19) 0.23 0.13 (0.06–0.32).........................................................................................................................

.37) 1.........................................................................................................................

.........................................................................................................................

(4.20) 0.24 0.20 (0.13–0.30).........................................................................................................................

7.40) 1.........................................................................................................................

.........................................................................................................................

(3.51) 0.23 0.18 (0.13–0.26).........................................................................................................................

5.08) 1.........................................................................................................................

etrical anal sphincter injuries; OR, odds ratio; RR, relative risk..

ge of epidural anesthesia, daytime obstetrics, birthweight �400

and OASIS. Am J Obstet Gynecol 2012.

reducing effect of the mediolateral epi-

MAY 2012 Americ

siotomy warrants its use in OVD, as op-posed to the use of median episiotomy,which has a marked risk, increasing ef-fect for the occurrence of OASIS inOVD.21

CONCLUSION

We found a 6-fold decreased odds for de-veloping OASIS when a MLE was per-formed during the operative vaginal de-livery. Therefore, we advocate the use ofa MLE in all operative vaginal deliveries

nd forcipal deliveries

cipal extraction (n � 316)

IS/n (%) RRAdjusteda OR(95% CI)

..................................................................................................................

54 (1.18) 0.05 0.02 (0.00–0.17)..................................................................................................................

6 (25) 1..................................................................................................................

..................................................................................................................

1 (2.44) 0.06 Not significant..................................................................................................................

(40) 1..................................................................................................................

..................................................................................................................

44 (1.23) 0.04 0.02 (0.00–0.13)..................................................................................................................

7 (29.4) 1..................................................................................................................

..................................................................................................................

5 (2.86) 0.06 Not significant..................................................................................................................

(50) 1..................................................................................................................

..................................................................................................................

8 (2.08) 0.02 Not significant..................................................................................................................

(100) 1..................................................................................................................

..................................................................................................................

0 (2.5) 0.04 Not significant..................................................................................................................

(60) 1..................................................................................................................

..................................................................................................................

18 (1.38) 0.03 0.02 (0.00–0.11)..................................................................................................................

4 (42.86) 1..................................................................................................................

..................................................................................................................

95 (1.36) 0.05 0.03 (0.00–0.14)..................................................................................................................

1 (20.57) 1..................................................................................................................

etal head position and prolonged pushing (�60 min).

r d s a

um For

S/n OAS

......... .........

50 3/2......... .........

3 (1 4/1......... .........

......... .........

4 (2 1/4......... .........

9 (1 2/5......... .........

......... .........

55 3/2......... .........

4 (1 5/1......... .........

......... .........

0 (5 1/3......... .........

(17 1/2......... .........

......... .........

6 (3 1/4......... .........

(14 1/1......... .........

......... .........

9 (5 1/4......... .........

(22 3/5......... .........

......... .........

81 3/2......... .........

9 (1 6/1......... .........

......... .........

96 4/2......... .........

4 (1 6/2......... .........

obst

, usa 0 g, f

to reduce the incidence of OASIS. f

an Journal of Obstetrics & Gynecology 404.e4

SMFM Papers www.AJOG.org

ACKNOWLEDGEMENTWe would like to acknowledge Mw Dr S. Tim-mermans for her assistance in the analysis.

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logists. The management of third and fourth de-

404.e5 American Journal of Obstetrics & Gynecolo

gree perineal tears. RCOG guideline no. 29.London: RCOG Press; 2007.9. Aukee P, Sundstrom H, Kairaluoma MV. Therole of mediolateral episiotomy during labour:analysis of risk factors for obstetric anal sphinc-ter tears. Acta Obstet Gynecol Scand 2006;85:856-60.10. Walsh CJ, Mooney EF, Upton GJ, MotsonRW. Incidence of third-degree perineal tears inlabour and outcome after primary repair. Br JSurg 1996;83:218-21.11. Carroli G, Mignini L. Episiotomy for vaginalbirth. Cochrane Database Syst Rev 2009:CD000081.12. Youssef R, Ramalingam U, Macleod M,Murphy DJ. Cohort study of maternal and neo-natal morbidity in relation to use of episiotomy atinstrumental vaginal delivery. BJOG 2005;112:941-5.13. Routine vs selective episiotomy: a ran-domised controlled trial. Argentine EpisiotomyTrial Collaborative Group. Lancet 1993;342:1517-8.14. Alperin M, Krohn MA, Parviainen K. Episiot-omy and increase in the risk of obstetric lacer-ation in a subsequent vaginal delivery. ObstetGynecol 2008;111:1274-8.15. Murphy DJ, Macleod M, Bahl R, Goyder K,Howarth L, Strachan B. A randomised con-trolled trial of routine versus restrictive use of

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multicentre pilot study. BJOG 2008;115:1695-702.16. Revicky V, Nirmal D, Mukhopadhyay S,Morris EP, Nieto JJ. Could a mediolateral epi-siotomy prevent obstetric anal sphincter injury?Eur J Obstet Gynecol Reprod Biol 2010;150:142-6.17. de Leeuw JW, de Wit C, Kuijken JP, BruinseHW. Mediolateral episiotomy reduces the riskfor anal sphincter injury during operative vaginaldelivery. BJOG 2008;115:104-8.18. Anthony S, van der Pal-de Bruin KM, Graaf-mans WC, et al. The reliability of perinatal andneonatal mortality rates: differential under-re-porting in linked professional registers vs. Dutchcivil registers. Paediatr Perinat Epidemiol 2001;15:306-14.19. Altman D, Carroli G, Duley L, et al. Dowomen with pre-eclampsia, and their babies,benefit from magnesium sulphate? The MagpieTrial: a randomised placebo-controlled trial.Lancet 2002;359:1877-90.20. Combs CA, Robertson PA, Laros RK Jr.Risk factors for third-degree and fourth-degreeperineal lacerations in forceps and vacuum de-liveries. Am J Obstet Gynecol 1990;163(1 Pt1):100-4.21. Kudish B, Blackwell S, Mcneeley SG, et al.Operative vaginal delivery and midline episiot-omy: a bad combination for the perineum. Am J

Obstet Gynecol 2006;195:749-54.