Rapidversusstepwisenegativepressureapplicationfor ... (rapid versus stepwise negative... ·...

Cochrane Database of Systematic Reviews

Rapid versus stepwise negative pressure application for

vacuum extraction assisted vaginal delivery (Review)

Suwannachat B, Lumbiganon P, Laopaiboon M

Suwannachat B, Lumbiganon P, Laopaiboon M.

Rapid versus stepwise negative pressure application for vacuum extraction assisted vaginal delivery.

Cochrane Database of Systematic Reviews 2012, Issue 8. Art. No.: CD006636.

DOI: 10.1002/14651858.CD006636.pub3.

www.cochranelibrary.com

Rapid versus stepwise negative pressure application for vacuum extraction assisted vaginal delivery (Review)

Copyright © 2012 The Cochrane Collaboration. Published by John Wiley & Sons, Ltd.

http://www.cochranelibrary.com

T A B L E O F C O N T E N T S

1HEADER . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .

1ABSTRACT . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .

2PLAIN LANGUAGE SUMMARY . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .

2BACKGROUND . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .

3OBJECTIVES . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .

3METHODS . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .

6RESULTS . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .

Figure 1. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 7

Figure 2. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 8

9DISCUSSION . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .

10AUTHORS’ CONCLUSIONS . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .

10ACKNOWLEDGEMENTS . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .

10REFERENCES . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .

11CHARACTERISTICS OF STUDIES . . . . . . . . . . . . . . . . . . . . . . . . . . . . .

16DATA AND ANALYSES . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .

Analysis 1.1. Comparison 1 Rapid versus stepwise negative pressure application, Outcome 1 Success rate of vacuum

procedure. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 16

Analysis 1.2. Comparison 1 Rapid versus stepwise negative pressure application, Outcome 2 Detachment rate. . . 17

Analysis 1.3. Comparison 1 Rapid versus stepwise negative pressure application, Outcome 3 Duration of vacuum extraction

procedure. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 18

Analysis 1.4. Comparison 1 Rapid versus stepwise negative pressure application, Outcome 4 Apgar score < 7 after 1

minute. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 18

Analysis 1.5. Comparison 1 Rapid versus stepwise negative pressure application, Outcome 5 Apgar score < 7 after 5

minutes. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 19

Analysis 1.6. Comparison 1 Rapid versus stepwise negative pressure application, Outcome 6 Scalp laceration > 1/4. . 19

Analysis 1.7. Comparison 1 Rapid versus stepwise negative pressure application, Outcome 7 Cephalhematoma. . . 20

Analysis 1.8. Comparison 1 Rapid versus stepwise negative pressure application, Outcome 8 Subgaleal hemorrhage. . 20

Analysis 1.9. Comparison 1 Rapid versus stepwise negative pressure application, Outcome 9 Hyperbilirubinemia. . 21

Analysis 1.10. Comparison 1 Rapid versus stepwise negative pressure application, Outcome 10 Second degree of perineal

tears. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 21

Analysis 1.11. Comparison 1 Rapid versus stepwise negative pressure application, Outcome 11 Third degree of perineal

tears. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 22

Analysis 1.12. Comparison 1 Rapid versus stepwise negative pressure application, Outcome 12 Umbilical venous pH <

7.2. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 22

Analysis 1.13. Comparison 1 Rapid versus stepwise negative pressure application, Outcome 13 Number of traction. . 23

Analysis 1.14. Comparison 1 Rapid versus stepwise negative pressure application, Outcome 14 Perineal pain after

delivery. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 23

Analysis 1.15. Comparison 1 Rapid versus stepwise negative pressure application, Outcome 15 Perineal wound infection. 24

Analysis 1.16. Comparison 1 Rapid versus stepwise negative pressure application, Outcome 16 Postpartum hemorrhage. 24

Analysis 1.17. Comparison 1 Rapid versus stepwise negative pressure application, Outcome 17 Perinatal death. . . 25

Analysis 1.18. Comparison 1 Rapid versus stepwise negative pressure application, Outcome 18 Obstetrician satisfaction. 25

Analysis 1.19. Comparison 1 Rapid versus stepwise negative pressure application, Outcome 19 Maternal satisfaction. 26

26APPENDICES . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .

27WHAT’S NEW . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .

28HISTORY . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .

28CONTRIBUTIONS OF AUTHORS . . . . . . . . . . . . . . . . . . . . . . . . . . . . .

28DECLARATIONS OF INTEREST . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .

28SOURCES OF SUPPORT . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .

29INDEX TERMS . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .

iRapid versus stepwise negative pressure application for vacuum extraction assisted vaginal delivery (Review)


[Intervention Review]

Rapid versus stepwise negative pressure application forvacuum extraction assisted vaginal delivery

Bunpode Suwannachat1 , Pisake Lumbiganon2 , Malinee Laopaiboon3

1Department of Obstetrics and Gynaecology, Kalasin Hospital, Amphur Muang, Thailand. 2Department of Obstetrics and Gynae-

cology, Faculty of Medicine, Khon Kaen University, Khon Kaen, Thailand. 3Department of Biostatistics and Demography, Faculty of

Public Health, Khon Kaen University, Khon Kaen, Thailand

Contact address: Bunpode Suwannachat, Department of Obstetrics and Gynaecology, Kalasin Hospital, 202/1 Thedban 23rd Road,

Amphur Muang, Kalasin Province, 46000, Thailand. [email protected].

Editorial group: Cochrane Pregnancy and Childbirth Group.

Publication status and date: New search for studies and content updated (conclusions changed), published in Issue 8, 2012.

Review content assessed as up-to-date: 8 May 2012.

Citation: Suwannachat B, Lumbiganon P, Laopaiboon M. Rapid versus stepwise negative pressure application for vac-

uum extraction assisted vaginal delivery. Cochrane Database of Systematic Reviews 2012, Issue 8. Art. No.: CD006636. DOI:10.1002/14651858.CD006636.pub3.


A B S T R A C T

Background

Vacuum extraction is a common technique of assisted vaginal delivery. Traditionally, it has been recommended that the pressure is

increased slowly in a stepwise procedure; some have advocated rapid increases in pressure.

Objectives

To assess the efficacy and safety of rapid versus stepwise negative pressure application for assisted vaginal delivery by vacuum extraction.

Search methods

We searched the Cochrane Pregnancy and Childbirth Group’s Trials Register (4 April 2012).

Selection criteria

Randomized controlled trials and quasi-randomized controlled trials of rapid (within two minutes) versus stepwise (as defined by

trialists) increases in negative pressure application for vacuum extraction assisted vaginal delivery.

Data collection and analysis

Two review authors independently assessed trials for inclusion and trial quality. The same two review authors extracted data. We entered

data into Review Manager software and checked for accuracy. Data extraction and ’Risk of bias’ assessment of the contact person’s own

study were also carried out by three independent assessors who were not involved in the new study.

Main results

We included two trials involving 754 participants.

One new trial of 660 participants showed the same success rate of vacuum procedure of 98.2% by both methods (risk ratio (RR) 1.00,

95% confidence interval (CI) 0.98 to 1.02).

The two included trials showed significant reductions in the time between applying the vacuum cup and delivery, (one trial (74 women):

mean difference (MD) -6.10 minutes, 95% CI -8.83 to -3.37 and the other trial (660 women): with median difference -4.4 minutes,

1Rapid versus stepwise negative pressure application for vacuum extraction assisted vaginal delivery (Review)


mailto:[email protected]

95% CI -4.8 to -4.0). The two included trials showed no significant difference in detachment rate (RR 0.85, 95% CI 0.38 to 1.86,

2 studies, 754 women), no significant difference in Apgar score below seven at one minute (RR 1.04, 95% CI 0.51 to 2.09) and

five minutes (RR 1.00, 95% CI 0.29 to 3.42), no significant differences in scalp abrasions or lacerations, cephalhematoma, subgaleal

hemorrhage and hyperbilirubinemia. There were no significant differences between the two methods in all secondary outcomes.

Authors’ conclusions

The rapid negative pressure application for vacuum assisted vaginal birth reduces duration of the procedure whilst there is no evidence of

differences in maternal and neonatal outcomes. Rapid method of negative application should be recommended for vacuum extraction

assisted vaginal delivery.

P L A I N L A N G U A G E S U M M A R Y

Applying negative pressure rapidly or in steps for vacuum extraction assisted vaginal delivery

Assisted vaginal delivery is an important part of obstetric care. Indications for its use include prolonged second stage of labour, actual

or potential fetal compromise or distress, and to shorten labour. The established methods facilitate the descent and birth of the infant.

A vacuum extractor is becoming the method of choice as it is less likely to injure the mother although failure of attempted vacuum

extraction may occur more often than with forceps. Rapid application addresses the benefit of vacuum extraction that can be used

when rapid delivery is required. Two good quality randomized controlled trials involving 754 women were identified. Rapid negative

pressure application reduced the duration of the procedure without any evidence of differences in outcomes for the mother or infant.

Rapid method of negative pressure application should be recommended for vacuum extraction assisted vaginal delivery.

B A C K G R O U N D

Historically, obstetricians have sought a method to assist vaginal

delivery, to grasp the fetal head in order to turn and manipulate

its position, and facilitate its descent and delivery. Assisted vaginal

delivery has become an integral part of obstetric care. Obstetric

forceps were the primary instruments used in assisting vaginal

delivery. However, more recently, forceps have been overtaken in

popularity in some countries by the vacuum extractor (Bofill

1996). In the United Kingdom, there has been an increasing use of

vacuum extraction compared with forceps extraction (O’Connell

2000; Patel 2004). The acceptance of the vacuum device as a

safe alternative to forceps was delayed in the USA compared with

European countries, but as of 1992, the rate of vacuum delivery

surpassed the rate of forceps delivery in the USA (Miksovsky

2001). Rates of vacuum extraction vary; approximately 10% in

the Middle East and Canada (Cargill 2004; Shihadeh 2001), 6%

in Australia (Laws 2005) and 8% in the USA (Kozak 2002).

Vacuum extraction is fast becoming the method of choice for

many assisted vaginal deliveries. Current evidence suggests that

when assisted vaginal delivery is required, the vacuum extraction

should often be chosen first, principally because it is significantly

less likely to injure the mother (Chalmers 1989; Johanson 1999),

although failure of attempted vacuum extraction will occur more

often than failed forceps delivery (Johanson 1999).

Indications for vacuum assisted delivery include prolonged sec-

ond stage of labour, suspicion of actual or potential fetal com-

promise, and to shorten the second stage of labour for maternal

benefit (ACOG 2000). The vacuum extractor is contraindicated

with face, brow or breech presentation. It has been suggested that

the vacuum extractor should not be used at gestations of less than

34 weeks because of the risk of cephalhematoma and intracranial

hemorrhage (RCOG 2005; Vacca 1999).

There is a traditional recommendation that, for vacuum cup ap-

plication, the operator should gradually increase negative pressure

at 0.2 kg/cm² every two minutes, to reach 0.8 kg/cm² over eight to

10 minutes. Theoretically, this process would allow the vacuum to

be firmly attached to the fetal head, thus decreasing the chance of

vacuum extraction failure (Malmstrom 1965). However, some ex-

perts suggest that this is both unnecessary and wastes time (Wider

1967). More recently, it has been suggested that there is no signif-

icant difference in the traction force developed between stepwise

and rapid application of the vacuum (Svenningsen 1987). Since

adequate chignon (temporary swelling on the infant’s scalp) forms

within one to two minutes of creating the vacuum and traction

may be commenced after one minute without compromising ef-



ficiency and safety (Guardino 1962; Lim 1997; Wider 1967). It

has been proposed that, for the soft cups, negative pressure could

be increased to 0.8 kg/cm² in as little as one minute (Kuit 1993).

Potential adverse effects of rapid application of vacuum extraction

include cup detachment and injury of the fetal scalp and blood

vessels.

The perception that vacuum extraction is too slow to be used

when rapid delivery is required (e.g. severe fetal distress) may not,

therefore, be supportable. In some countries, most obstetricians

still use the stepwise negative pressure application, in the belief

that this prevents cup detachment. We systematically evaluated

whether there are any differences in efficacy and safety in rapid

versus stepwise negative pressure application for vacuum assisted

vaginal delivery.

Readers may wish to refer to the following Cochrane systematic

review for further information on vacuum extraction for assisted

vaginal deliveries:’Choice of instruments for assisted vaginal delivery’(O’Mahony 2010).

O B J E C T I V E S

To assess efficacy and safety of rapid versus stepwise negative pres-

sure application for assisted vaginal delivery by vacuum extraction.

M E T H O D S

Criteria for considering studies for this review

Types of studies

Randomized controlled trials and quasi-randomized controlled

trials.

Types of participants

Women undergoing vacuum extraction assisted vaginal delivery.

Types of interventions

Rapid (within two minutes) versus stepwise (as defined by trial-

ists) negative pressure application for vacuum extraction assisted

vaginal delivery.

Types of outcome measures

Primary outcomes

(1) Maternal1. Success or failure rate of vacuum procedure

2. Detachment rate

3. Duration of vacuum extraction procedure

4. Birth passage injury including degree of perineal tears,

cervical and uterine tears

5. Actual mode of delivery

(2) Fetal1. Birth asphyxia (according to trialists’ definition)

2. Fetal injury including scalp abrasions or lacerations, caput

succedaneum, cephalhematoma, subgaleal hemorrhage,

intracranial injury (rely on trialists’ definition)

3. Hyperbilirubinemia

Secondary outcomes

(1) Maternal1. Perineal pain after delivery

2. Perineal wound infection

3. Rectovaginal fistula

4. Postpartum hemorrhage

(2) Fetal1. Retinal hemorrhage

2. Breastfeeding failure

3. Perinatal death

(3) Obstetrician satisfaction

(4) Maternal satisfaction

Search methods for identification of studies

Electronic searches

We searched the Cochrane Pregnancy and Childbirth Group’s Tri-

als Register by contacting the Trials Search Co-ordinator (4 April

2012).

The Cochrane Pregnancy and Childbirth Group’s Trials Register

is maintained by the Trials Search Co-ordinator and contains trials

identified from:

1. monthly searches of the Cochrane Central Register of

Controlled Trials (CENTRAL);

2. weekly searches of MEDLINE;

3. weekly searches of EMBASE;

4. handsearches of 30 journals and the proceedings of major

conferences;

5. weekly current awareness alerts for a further 44 journals

plus monthly BioMed Central email alerts.



Details of the search strategies for CENTRAL, MEDLINE and

EMBASE, the list of handsearched journals and conference pro-

ceedings, and the list of journals reviewed via the current aware-

ness service can be found in the ‘Specialized Register’ section

within the editorial information about the Cochrane Pregnancy

and Childbirth Group.

Trials identified through the searching activities described above

are each assigned to a review topic (or topics). The Trials Search

Co-ordinator searches the register for each review using the topic

list rather than keywords.

We did not apply any language restrictions.

Data collection and analysis

For the methods used when assessing the trials identified in the

previous version of this review, see Appendix 2.For this update we used the following methods when assessing the

reports identified by the updated search.

Selection of studies

Two review authors independently assessed for inclusion all the

potential studies we identified as a result of the search strategy. We

resolved any disagreement through discussion.

Data extraction and management

We designed a form to extract data. For eligible studies, two review

authors (B Suwannachat (BS), M Laopaiboon (ML)) extracted the

data using the agreed form. We also invited three independent

assessors who were not involved in the new trial to extract data. We

resolved discrepancies through discussion or consulted the third

review author (P Lumbiganon (PL)). We entered data into Review

Manager software (RevMan 2011) and checked for accuracy.

Assessment of risk of bias in included studies

Two review authors (BS, ML) and the invited colleagues indepen-

dently assessed risk of bias for each study using the criteria outlined

in the Cochrane Handbook for Systematic Reviews of Interventions(Higgins 2011), except blinding because it is not possible to blind

the operators, outcome assessors and pregnant women about the

vacuum applications. We resolved any disagreement by discussionor consulted the third review author (PL).

(1) Random sequence generation

We described for each included study the method used to generate

the allocation sequence in sufficient detail to allow an assessment

of whether it should produce comparable groups.

We assessed the method as:

• low risk of bias (any truly random process, e.g. random

number table; computer random number generator);

• high risk of bias (any non-random process, e.g. odd or even

date of birth; hospital or clinic record number);

• unclear risk of bias.

(2) Allocation concealment

We described for each included study the method used to con-

ceal allocation to interventions prior to assignment and assessed

whether intervention allocation could have been foreseen in ad-

vance of, or during recruitment, or changed after assignment.

We assessed the methods as:

• low risk of bias (e.g. telephone or central randomization;

consecutively numbered sealed opaque envelopes);

• high risk of bias (open random allocation; unsealed or non-

opaque envelopes, alternation; date of birth);


(3.1) Blinding of participants and personnel (checking for

possible performance bias)

We did not assess performance bias because for the rapid and

stepwise methods of vacuum extraction. It is not possible to blind

obstetricians and pregnant women.

(3.2) Blinding of outcome assessment (checking for possible

detection bias)

We described for each included study the methods used, if any, to

blind outcome assessors from knowledge of which intervention a

participant received. We planned to assess blinding separately for

different outcomes or classes of outcomes.

We assessed methods used to blind outcome assessment as:

• low, high or unclear risk of bias.

(4) Incomplete outcome data

We described for each included study, and for each outcome the

completeness of data including attrition and exclusions from the

analysis. We stated whether attrition and exclusions were reported

and the numbers included in the analysis at each stage , reasons for

attrition or exclusion where reported, and whether missing data

were balanced across groups related to outcomes.

We assessed methods as:

• low risk of bias (e.g. no missing outcome data; missing

outcome data balanced across groups);

• high risk of bias (e.g. numbers or reasons for missing data

imbalanced across groups; ‘as treated’ analysis done with

substantial departure of intervention received from that assigned

at randomization);




http://www.mrw.interscience.wiley.com/cochrane/clabout/articles/PREG/frame.htmlhttp://www.mrw.interscience.wiley.com/cochrane/clabout/articles/PREG/frame.htmlhttp://www.mrw.interscience.wiley.com/cochrane/clabout/articles/PREG/frame.htmlhttp://www.mrw.interscience.wiley.com/cochrane/clabout/articles/PREG/frame.htmlhttp://www.mrw.interscience.wiley.com/cochrane/clabout/articles/PREG/frame.html

(5) Selective reporting

We described for each included study how we investigated the

possibility of selective outcome reporting bias and what we found.

We assessed the methods as:

• low risk of bias (where it is clear that all of the study’s pre-

specified outcomes and all expected outcomes of interest to the

review have been reported);

• high risk of bias (where not all the study’s pre-specified

outcomes have been reported; one or more reported primary

outcomes were not pre-specified; outcomes of interest are

reported incompletely and so cannot be used; study fails to

include results of a key outcome that would have been expected

to have been reported);


(6) Other bias

We described for each included study any important concerns we

had about other possible sources of bias.

We assessed whether each study was free of other problems that

could put it at risk of bias:

• low risk of other bias; (where balance baseline

characteristics between the two methods);

• high risk of other bias; (where imbalance baseline

characteristics between the two methods);

• unclear whether there is risk of other bias.

(7) Overall risk of bias

We made explicit judgements about whether studies were at high

risk of bias, according to the criteria given in the Handbook (Higgins 2011). With reference to (1) to (5) above, we assessed

the likely magnitude and direction of the bias and whether we

considered it was likely to impact on the findings.

Measures of treatment effect

Dichotomous data

For dichotomous data such as success of vacuum procedure, we

presented results as summary risk ratio with 95% confidence in-

tervals.

Continuous data

For continuous data, we used the mean difference if outcomes

were measured in the same way between trials. We planned to use

the standardized mean difference to combine trials that measured

the same outcome, but used different methods.

Unit of analysis issues

Cluster-randomized trials

We did not include cluster-randomized trials. We, therefore, were

not aware of any unit of analysis issues.

Dealing with missing data

For included studies, we noted levels of attrition.

For all outcomes, we carried out analyses, as far as possible, on

an intention-to-treat basis, i.e. we attempted to include all partic-

ipants randomized to each group in the analyses, and all partici-

pants were analyzed in the group to which they were allocated, re-

gardless of whether or not they received the allocated intervention.

The denominator for each outcome in each trial was the number

randomized minus any participants whose outcomes were known

to be missing.

Assessment of heterogeneity

We assessed statistical heterogeneity in each meta-analysis using

the T², I² and Chi² statistics. We regarded heterogeneity as sub-

stantial if the I² was greater than 30% and either the T² was greater

than zero, or there was a low P value (less than 0.10) in the Chi²

test for heterogeneity.

Assessment of reporting biases

We did not assess the reporting biases because there were only two

included studies.

Data synthesis

We carried out statistical analysis using the Review Manager soft-

ware (RevMan 2011). We used fixed-effect meta-analysis for com-

bining data where it was reasonable to assume that studies were

estimating the same underlying treatment effect: i.e. where trials

were examining the same intervention, and the trials’ populations

and methods were judged sufficiently similar. If there was clinical

heterogeneity sufficient to expect that the underlying treatment ef-

fects differed between trials, or if substantial statistical heterogene-

ity was detected, we used random-effects meta-analysis to produce

an overall summary if an average treatment effect across trials was

considered clinically meaningful. We treated the random-effects

summary as the average range of possible treatment effects and we

discussed the clinical implications of treatment effects differing

between trials.



Subgroup analysis and investigation of heterogeneity

In future updates, if more trials are identified, we will explore any

substantial heterogeneity identified using subgroup analyses and

sensitivity analyses. We will consider whether an overall summary

is meaningful, and if it is, we will use a random-effects analysis to

produce it.

We plan, where possible, to carry out the following subgroup anal-

yses.

• Indications for vacuum.

• Operator experience.

The following primary outcomes will be considered in subgroup

analysis.

For Maternal

• Success rate of vacuum procedure.

• Detachment rate.

For Fetal

• Birth asphyxia.

• Fetal injury including scalp abrasions or lacerations, caput

succedaneum, cephalhematoma, subgaleal hemorrhage,

intracranial injury.

We will assess subgroup differences by interaction tests available

within RevMan (RevMan 2011).

Sensitivity analysis

In future updates, if more trials are identified, we plan to carry out

sensitivity analyses to explore the effect of trial quality assessed by

concealment of allocation, high attrition rates, or both, with poor

quality studies being excluded from the analyses in order to assess

whether this makes any difference to the overall result.

R E S U L T S

Description of studies

Results of the search

In our first published version of this review (Suwannachat 2008),

we identified two studies as potentially eligible for inclusion in

this review. We excluded one study (Svenningsen 1987) - see tableof Characteristics of excluded studies. A single trial of 94 women

met the selection criteria (Lim 1997) - see table of Characteristicsof included studies for full details.

In this update we searched the Pregnancy and Childbirth Group’s

Trials Register and included one more trial (Suwannachat 2011).

Included studies

In this updated version, we included a total of two trials involving

754 pregnant women. Details of the included trials are provided

in the table of Characteristics of included studies.

Study location

The two included trials were in English. However, one trial (Lim

1997) was performed in the Netherlands between August 1992

and December 1993, and another trial (Suwannachat 2011) was

performed in Thailand between January 2009 and April 2010.

Participants

One trial (Lim 1997) was undertaken with pregnant women who

had an indication of prolonged second stage of labour while the

other (Suwannachat 2011) included women with various indi-

cations but approximately 68% of them were experiencing pro-

longed second stage of labour or maternal exhaustion.

Intervention

The two included trials compared rapid with conventional step-

wise methods of negative pressure in vacuum extraction assisted

vaginal delivery.

Excluded studies

We excluded one study because it was neither a randomized con-

trolled trial nor a quasi-randomized controlled trial (Svenningsen

1987) - see table of Characteristics of excluded studies.

Risk of bias in included studies

Details of the risk of bias of each study are given in the ’Risk of bias’

tables of the Characteristics of included studies table. The overall

risk of bias is presented graphically in Figure 1 and summarized

in Figure 2.



Figure 1. ’Risk of bias’ graph: review authors’ judgements about each risk of bias item presented as

percentages across all included studies.



Figure 2. ’Risk of bias’ summary: review authors’ judgements about each risk of bias item for each included

study.

Allocation

The two included trials (Lim 1997; Suwannachat 2011) had ade-

quate sequence generation for randomization and allocation con-

cealment. They were assessed as low risk for selection bias.

Blinding

It was not possible to blind the obstetricians and pregnant women

to the rapid and stepwise methods of vacuum extraction proce-

dure. It is possible to blind an outcome assessor to the interven-

tions. One trial (Lim 1997) reported that the outcome variables

were recorded by the obstetrician one hour after birth between the

third and the fifth day after birth. A physical examination of the

infant was performed by a pediatrician who paid attention to pos-

sible neonatal morbidity associated with ventouse extraction pro-

cedures. The pediatrician was not aware of the manner in which

the vacuum had been applied. This implies that there could have

been outcome assessment bias on the part of the obstetrician. The

other trial (Suwannachat 2011), did not provide information of

processes and assessors of the primary and secondary outcomes.

We assessed the trial as unclear for detection bias.



Incomplete outcome data

Most of the outcomes were measured just after delivery. Loss to

follow-up was not an issue in the trials. However, one trial (Lim

1997) reported some infant outcomes in the 73 available children

(77.7%). In 21 missing cases, the parents did not return with their

child to the outpatient clinic: 10 in the rapid group and 11 in

the stepwise group. The other trial (Suwannachat 2011), did not

record outcome data for two participants (one in rapid, one in

stepwise) because both were antepartum fetal deaths.

Selective reporting

We could not consider study protocol of one trial (Lim 1997)

and we assessed it as unclear for reporting bias. The other trial

(Suwannachat 2011) reported all outcomes as planned in the study

protocol.

Other potential sources of bias

The two trials had similar baseline characteristics between the two

methods of vacuum extraction procedure. We assessed them as

low risk for other potential sources of bias.

Overall, we considered the two included trials to be at low risk of

bias.

Effects of interventions

We included two trials with 754 pregnant women providing data

for analysis in this updated version.

Primary outcomes: maternal

Success rate of vacuum procedure

Only one new included trial (Suwannachat 2011) involving 660

women report the same success rate of vacuum procedure of 98.2

% for each method (risk ratio (RR) 1.00, 95% confidence interval

(CI) 0.98 to1.02) (Analysis 1.1).

Detachment rate

The two included trials (754 women) provided no significant

difference of pooled detachment rates between the two methods

(pooled RR 0.85, 95% CI 0.38 to 1.86) (Analysis 1.2).

Duration of vacuum extraction procedure

The two included trials reported a significant reduction in the du-

ration of the vacuum extraction procedure in the women receiving

the rapid method of vacuum application. In one trial (Lim 1997)

there was a mean difference (MD) of -6.10 minutes (95% CI -

8.83 to -3.37; 74 women) (Analysis 1.3). The other trial involv-

ing 660 women (Suwannachat 2011), reported a median (range)

duration of 5.5 minutes (1.3, 44.3) in the rapid method group

and 10 minutes (1.9, 26) in the stepwise method group, with a

median difference of -4.4 (95%CI -4.8, -4.0).

Primary outcomes: fetal

Birth asphyxia

The two included trials with 754 pregnant women showed no

significant differences between the two methods in Apgar score

less than seven at one minute (pooled RR 1.04, 95% CI 0.51 to

2.09) ( Analysis 1.4) and five minutes (pooled RR 1.00, 95% CI

0.29 to 3.42) (Analysis 1.5).

Fetal injury

The were no significant differences between the two methods

in scalp abrasions or lacerations (Analysis 1.6) from one trial

(Lim 1997) with 73 babies; cephalhematoma (Analysis 1.7) from

the two included trials with 733 babies; subgaleal hemorrhage

(Analysis 1.8) and hyperbilirubinemia (Analysis 1.9) from one trial

(Suwannachat 2011) with 660 babies.

Secondary outcomes

There were no significant differences between the two methods in

all other outcomes as shown in Analysis 1.10 to Analysis 1.19.

D I S C U S S I O N

Summary of main results

This review indicates that there are no significant differences in

maternal and neonatal outcomes between rapid and stepwise neg-

ative pressure application for vacuum assisted vaginal birth. How-

ever, the rapid method can reduce the duration of vacuum extrac-

tion procedure by four to six minutes.

Overall completeness and applicability ofevidence

The two included trials were from both developed (The Nether-

land) and developing (Thailand) countries. The trial from Thai-

land was a multicentre trial with six participating hospitals that

were secondary and tertiary care centers. Applicability of the evi-

dence is therefore quite reasonable.



Quality of the evidence

The two included trials involving 754 pregnant women had ad-

equate random allocation concealment and low risk of attrition

bias and selective reporting. Risk of detection bias was unclear.

However, both trials reported all important outcomes and the re-

sults were in the same direction. The overall evidence of the two

included trials is therefore reasonably valid.

Potential biases in the review process

We strictly followed the review process recommended by the Preg-

nancy and Childbirth Review Group. For this update, we included

our trial to this review. However, we asked three of our colleagues

who were not involved in our trial to carry out the risk assessment

and extract data for us. It is therefore unlikely to have any bias in

the review process.

Agreements and disagreements with otherstudies or reviews

There are no other studies or reviews on this topic.

A U T H O R S ’ C O N C L U S I O N S

Implications for practice

Rapid method of negative pressure application should be recom-

mended for vacuum assisted vaginal birth.

Implications for research

No more research on this issue is required.

A C K N O W L E D G E M E N T S

We would like to thank the SEA ORCHID project for building

capacity in research synthesis, thanks to Prof Jim Neilson, Sonja

Henderson and Gill Gyte, Cochrane Pregnancy and Childbirth

Group, for supervising the completion of the review.

Thanks also to Jadsada Thinkhumlop, Ussanee Sawaddipanich

and Porjai Pattanittum for carrying out the ’Risk of bias’ assessment

and data extraction at the update stage.

R E F E R E N C E S

References to studies included in this review

Lim 1997 {published data only}

Lim FTH, Holm JP, Schuitemaker NW, Jansen FH,

Hermans J. Stepwise compared with rapid application of

vacuum in ventouse extraction procedures. British Journal

of Obstetrics and Gynaecology 1997;104:33–6.

Suwannachat 2011 {published data only}

Suwannachat B, Laopaiboon M, Tonmat S, Siriwachirachai

T, Teerapong S, Winiyakul N, et al. Rapid versus stepwise

application of negative pressure in vacuum extraction-

assisted vaginal delivery: A multicentre randomised

controlled non-inferiority trial. BJOG: an international

journal of obstetrics and gynaecology 2011;118(10):1247–52.

References to studies excluded from this review

Svenningsen 1987 {published data only}

Svenningsen L. Birth progression and traction forces

developed under vacuum extraction after slow or rapid

application of suction. European Journal of Obstetrics &

Gynecology and Reproductive Biology 1987;26:105–12.

Additional references

ACOG 2000

American College of Obstetricians and Gynecologists.

Operative vaginal delivery: use of forceps and vacuum extractors

for operative vaginal delivery. ACOG Practice Bulletin. Vol.

17, Washington DC: ACOG, 2000.

Bofill 1996

Bofill JA, Perry KG, Roberts WE, Martin RW, Morrison JC,

Rust OA. Forceps and vacuum delivery: a survey of North

American residency programs. Obstetrics & Gynecology

1996;88(4 Pt 1):622–5.

Cargill 2004

Cargill YM, MacKinnon CJ, Arsenault MY, Bartellas E,

Daniels S, Gleason T, et al. Guidelines for operative vaginal

birth. Journal of Obstetrics and Gynaecology Canada: JOGC

2004;26(8):747–61.

Chalmers 1989

Chalmers JA, Chalmers I. The obstetric vacuum extractor is

the instrument of first choice for operative vaginal delivery.

British Journal of Obstetrics and Gynaecology 1989;96:505–9.

Deeks 2001

Deeks JJ, Altman DG, Bradbury MJ. Statistical methods

for examining heterogeneity and combining results from

several studies in meta-analysis. In: Egger M, Davey Smith

G, Altman DG editor(s). Systematic reviews in health care:

meta-analysis in context. London: BMJ Books, 2001.

Egger 1997

Egger M, Davey Smith G, Schneider M, Minder CE. Bias

in meta-analysis detected by a simple, graphical test. BMJ

1997;315:629–34.



Guardino 1962

Guardino AN, Brien FB. Preliminary experience with

Malmstrom’s vacuum extractor. American Journal of

Obstetrics and Gynecology 1962;83(3):300–6.

Higgins 2005

Higgins JP, Green S, editors. Cochrane Handbook for

Systematic Reviews of Interventions 4.2.4 [updated

March 2005]. In: The Cochrane Library, Issue 2, 2005.

Chichester, UK: John Wiley & Sons, Ltd.

Higgins 2011

Higgins JPT, Green S, editors. Cochrane Handbook for

Systematic Reviews of Interventions Version 5.1.0 [updated

March 2011]. The Cochrane Collaboration, 2011.

Available from www.cochrane-handbook.org.

Johanson 1999

Johanson RB, Menon V. Vacuum extraction versus

forceps for assisted vaginal delivery. Cochrane Database

of Systematic Reviews 1999, Issue 2. [DOI: 10.1002/

14651858.CD000224]

Kozak 2002

Kozak LJ, Weeks JD. U.S. trends in obstetric procedures,

1990-2000. Birth 2002;29:157–61.

Kuit 1993

Kuit JA, Eppinga HG, Wallenburge HC, Huikeshoven FJ.

A randomized comparison of vacuum extraction delivery

with a rigid and a pliable cup. Obstetrics & Gynecology 1993;

82(2):280–4.

Laws 2005

Laws PJ, Sullivan EA. Australia’s mothers and babies 2003.

Sydney: AIHW National Perinatal Statistics Unit, 2005.

Malmstrom 1965

Malmstrom T, Jansson I. Use of the vacuum extractor.

Clinical Obstetrics and Gynecology 1965;8:893–913.

Miksovsky 2001

Miksovsky P, Watson WJ. Obstetric vacuum extraction:

state of the art in the new millennium. Obstetrical &

Gynecological Survey 2001;56:736–51.

O’Connell 2000

O’Connell SW, Lindow M. Trends in obstetric care in the

United Kingdom. Journal of Obstetrics and Gynaecology

2000;20:592–3.

O’Mahony 2010

O’Mahony F, Hofmeyr GJ, Menon V. Choice of

instruments for assisted vaginal delivery. Cochrane Database


14651858.CD005455.pub2]

Patel 2004

Patel RR, Murphy DJ. Forceps delivery in modern obstetric

practice. BMJ 2004;328:1302–5.

RCOG 2005

Royal College of Obstetricians and Gynaecologists.

Operative Vaginal Delivery. Clinical Green Top Guidelines

(Guideline No. 26). London: RCOG, 2005.

RevMan 2003 [Computer program]

The Cochrane Collaboration. Review Manager (RevMan).

Version 4.2 for Windows. Oxford, England: The Cochrane

Collaboration, 2003.

RevMan 2011 [Computer program]

The Nordic Cochrane Centre, The Cochrane Collaboration.

Review Manager (RevMan). Version 5.1. Copenhagen:

The Nordic Cochrane Centre, The Cochrane Collaboration,

2011.

Shihadeh 2001

Shihadeh A, Al-Najdawi W. Forceps or vacuum extraction:

a comparison of maternal and neonatal morbidity. Eastern

Mediterranean Health Journal 2001;7:106–14.

Vacca 1999

Vacca A. The trouble with vacuum extraction. Current

Obstetrics & Gynaecology 1999;9:41–5.

Wider 1967

Wider JA, Erez S, Steer CM. An evaluation of the vacuum

extractor in a series of 201 cases. American Journal of

Obstetrics and Gynecology 1967;98:24–31.

References to other published versions of this review

Suwannachat 2008

Suwannachat B, Lumbiganon P, Laopaiboon M. Rapid

versus stepwise negative pressure application for vacuum

extraction assisted vaginal delivery. Cochrane Database


14651858.CD006636.pub2]∗ Indicates the major publication for the study



C H A R A C T E R I S T I C S O F S T U D I E S

Characteristics of included studies [ordered by study ID]

Lim 1997

Methods Randomized controlled trial using sealed envelopes in blocks of 10.

No pretrial sample size given.

Participants 94 women eligible for the study were those with an uncomplicated singleton pregnancy

of more than 37 weeks of gestation, with a cephalic presentation. Instrumental vaginal

delivery was indicated due to prolonged second stage of labour (defined as at least 1 hour

of active expulsive efforts) without signs of fetal distress.

8% of eligible women were excluded.

Interventions Ventouse extraction procedures were performed by application to the fetal head of a

metal cup (Malmstrom, 50 mm) connected to an automatic electric pump (Egnell com-

pact 5, Ameda, Cary, Illinois, USA). The conventional stepwise method consisted of 4

incremental steps of 0-2 kg/cm2 every 2 min to obtain a final negative pressure of 0-8

kg/cm2. In the rapid method the negative pressure of 0-8 kg/cm2 was applied in 1 step.

When the final pressure had been achieved, traction was undertaken during uterine con-

tractions and maternal expulsive efforts. If there was detachment of the ventouse cup, it

was applied again to the fetal head in the manner indicated by the initial randomization

Outcomes Duration of the complete procedure, The number of detachment of the cup, Apgar scores

at 1 min and 5 min, and acid-base status of venous cord blood, superficial scalp lesions,

cephalhematomas and clinical jaundice, serum bilirubin concentration, Scalp lesions

were scored according to the extent of the fetal scalp involved: < 1/4, 1/4 to 3/4 or > 3/

4 of the surface. The neurological condition of the child was determined by the Sarnat

score, including crying, irritability and feeding problems, and a physical neurological

examination. The Sarnat score runs from 0 (normal) to 4 (severe neurological damage)

Notes Follow-up data were available on 73 children. In 21 cases the parents did not return with

their child to the outpatient clinic: 10 in the rapid group and 11 in the stepwise group.

Sarnat score < 0 was not prespecified in the protocol for this review. There was no low

Sarnat score in either group so RR would not be calculated

Risk of bias

Bias Authors’ judgement Support for judgement

Random sequence generation (selection

bias)

Unclear risk No information of random sequence gen-

eration used.

Allocation concealment (selection bias) Low risk Randomization was performed using sealed

envelopes in blocks of 10

Blinding of participants and personnel

(performance bias)

All outcomes

High risk The rapid or stepwise negative pressure

method cannot be blinded because the time



Lim 1997 (Continued)

for operating the two procedures are differ-

ent

Blinding of outcome assessment (detection

bias)

All outcomes

Low risk Quote - “The pediatrician was not aware of

the manner in which the vacuum had been

applied.”

Incomplete outcome data (attrition bias)

All outcomes

Low risk Outcomes were measured at delivery and

no missing data occurred

Selective reporting (reporting bias) Low risk Comment - follow-up data were available

on 73 children. In 21 cases the parents did

not return with their child to outpatients

clinic

Other bias Low risk No other obvious biases

Suwannachat 2011

Methods A hospital-based multicentre randomized controlled trial in 6 obstetric departments of

the participating centres in Thailand. Lists of random allocation stratified by hospital

were generated using online calculators for scientists and packed in opaque and sealed

envelopes

Consenting women needing delivery by vacuum extraction were randomly allocated to

the rapid or stepwise negative pressure method just before delivery

Participants 662 eligible singleton pregnancies admitted to the labour rooms of the participating

hospitals were randomly assigned to each intervention between January 2009 and April

2010. They also had indication for vacuum extraction at gestational age > 34 weeks and

babies in cephalic presentation. They were was not refusal to giving informed consent;

entitled to give informed consent; and severe fetal distress (as defined by the attending

doctors)

Analysis was done in 660 pregnant women because 2 had antepartum fetal deaths (1 in

each intervention group)

Interventions Vacuum extraction procedure was performed with a metal cup (Malmstrom) connected

to an electric pump applied to the fetal head. The cup was also used for occiput anterior

and posterior deliveries. The conventional stepwise method consisted of four incremental

steps of 0.2 kg/cm2 every 2 minutes to obtain a final negative pressure of 0.8 kg/cm2. In

the rapid method, the negative pressure of 0.8 kg/cm2 was applied in 1 step in < 2 min.

When the final pressure was achieved, traction was undertaken during uterine contrac-

tions and maternal expulsive efforts. When cup detachment occurred, it was applied

again if clinically appropriate. But no more than two detachments were allowed. Epi-

siotomy was used selectively

Outcomes The primary outcome was the success rate of vacuum extraction after the first application.

The secondary outcomes for mothers were: vacuum cup detachment rate; overall success

rate of vacuum extraction procedure; duration of vacuum extraction procedure; birth

passage injury (including degree of perineal tears, and cervical and uterine tears); actual



Suwannachat 2011 (Continued)

mode of delivery; postpartum hemorrhage; perineal pain after delivery; and perineal

wound infection prior to discharge. The neonatal outcomes included: birth asphyxia

(Apgar score < 7 at 5 mins after birth); fetal injury (including scalp abrasions or lacera-

tions, caput succedaneum, cephalhematoma, subgaleal hemorrhage, intracranial injury,

and subarachnoid, subdural, epidural, cerebral and cerebellar hemorrhage); hyperbiliru-

binemia; retinal hemorrhage; perinatal death; and obstetrician and maternal satisfaction

measured on a visual analogue scale of 0-10, and classified as poor (< 3), satisfactory (3-

6) or excellent (7-10)

Notes

Risk of bias

Bias Authors’ judgement Support for judgement

Random sequence generation (selection

bias)

Low risk Quote - “The simple random allocation se-

quence was generated using online calcu-

lators for scientists.20 These simple ran-

domisations were stratified by hospital”

Allocation concealment (selection bias) Low risk Quote - “Opaque, sealed, sequentially

numbered envelopes were used to conceal

the allocation. Consented participants who

needed to be delivered by vacuum extrac-

tion were randomly allocated to the rapid

or stepwise negative pressure method just

before delivery”

Blinding of participants and personnel

(performance bias)

All outcomes

High risk Comment - the rapid or stepwise negative

pressure method can not be blinded be-

cause the time for operating the two proce-

dures are different

Blinding of outcome assessment (detection

bias)

All outcomes

Low risk Comment - the outcome assessors were not

blinded. However, outcomes in the study

were mainly objective outcomes; this al-

lowed us to consider the trial to be low risk

in detection bias

Incomplete outcome data (attrition bias)

All outcomes

Low risk Outcomes were measured at delivery and

no missing data occurred

Selective reporting (reporting bias) Low risk Comment - Although the number of

women included in analysis was 660 (from

662), there was a clear report of the 2 ex-

cluded cases

Other bias Low risk No other obvious biases



min: minutes

RR: risk ratio

Characteristics of excluded studies [ordered by study ID]

Study Reason for exclusion

Svenningsen 1987 This study was not a clinical trial.



D A T A A N D A N A L Y S E S

Comparison 1. Rapid versus stepwise negative pressure application

Outcome or subgroup titleNo. of

studies

No. of

participants Statistical method Effect size

1 Success rate of vacuum procedure 1 Risk Ratio (M-H, Fixed, 95% CI) Totals not selected

2 Detachment rate 2 754 Risk Ratio (M-H, Fixed, 95% CI) 0.85 [0.38, 1.86]

3 Duration of vacuum extraction

procedure

1 Mean Difference (IV, Fixed, 95% CI) Totals not selected

4 Apgar score < 7 after 1 minute 2 754 Risk Ratio (M-H, Random, 95% CI) 1.04 [0.51, 2.09]

5 Apgar score < 7 after 5 minutes 2 754 Risk Ratio (M-H, Fixed, 95% CI) 1.0 [0.29, 3.42]

6 Scalp laceration > 1/4 1 Risk Ratio (M-H, Fixed, 95% CI) Totals not selected

7 Cephalhematoma 2 733 Risk Ratio (M-H, Random, 95% CI) 0.67 [0.30, 1.53]

8 Subgaleal hemorrhage 1 Risk Ratio (M-H, Fixed, 95% CI) Totals not selected

9 Hyperbilirubinemia 1 Risk Ratio (M-H, Fixed, 95% CI) Totals not selected

10 Second degree of perineal tears 1 Risk Ratio (M-H, Fixed, 95% CI) Totals not selected

11 Third degree of perineal tears 2 754 Risk Ratio (M-H, Fixed, 95% CI) 1.35 [0.83, 2.19]

12 Umbilical venous pH < 7.2 1 Risk Ratio (M-H, Fixed, 95% CI) Totals not selected

13 Number of traction 1 Mean Difference (IV, Fixed, 95% CI) Totals not selected

14 Perineal pain after delivery 1 Risk Ratio (M-H, Fixed, 95% CI) Totals not selected

15 Perineal wound infection 1 Risk Ratio (M-H, Fixed, 95% CI) Totals not selected

16 Postpartum hemorrhage 1 Risk Ratio (M-H, Fixed, 95% CI) Totals not selected

17 Perinatal death 1 Risk Ratio (M-H, Fixed, 95% CI) Totals not selected

18 Obstetrician satisfaction 1 Risk Ratio (M-H, Fixed, 95% CI) Totals not selected

19 Maternal satisfaction 1 Risk Ratio (M-H, Fixed, 95% CI) Totals not selected

Analysis 1.1. Comparison 1 Rapid versus stepwise negative pressure application, Outcome 1 Success rate of

vacuum procedure.

Review: Rapid versus stepwise negative pressure application for vacuum extraction assisted vaginal delivery

Comparison: 1 Rapid versus stepwise negative pressure application

Outcome: 1 Success rate of vacuum procedure

Study or subgroup Rapid application Stepwise application Risk Ratio Risk Ratio

n/N n/N M-H,Fixed,95% CI M-H,Fixed,95% CI

Suwannachat 2011 324/330 324/330 1.00 [ 0.98, 1.02 ]

0.5 0.7 1 1.5 2

Favours stepwise Favours rapid



Analysis 1.2. Comparison 1 Rapid versus stepwise negative pressure application, Outcome 2 Detachment

rate.



Outcome: 2 Detachment rate

Study or subgroup Rapid application Stepwise application Risk Ratio Weight Risk Ratio


Lim 1997 2/47 3/47 23.1 % 0.67 [ 0.12, 3.81 ]

Suwannachat 2011 9/330 10/330 76.9 % 0.90 [ 0.37, 2.19 ]

Total (95% CI) 377 377 100.0 % 0.85 [ 0.38, 1.86 ]

Total events: 11 (Rapid application), 13 (Stepwise application)

Heterogeneity: Chi2 = 0.09, df = 1 (P = 0.76); I2 =0.0%

Test for overall effect: Z = 0.41 (P = 0.68)

Test for subgroup differences: Not applicable

0.002 0.1 1 10 500

Favours rapid Favours stepwise



Analysis 1.3. Comparison 1 Rapid versus stepwise negative pressure application, Outcome 3 Duration of

vacuum extraction procedure.



Outcome: 3 Duration of vacuum extraction procedure

Study or subgroup Rapid application Stepwise applicationMean

DifferenceMean

Difference

N Mean(SD) N Mean(SD) IV,Fixed,95% CI IV,Fixed,95% CI

Lim 1997 47 7.8 (8) 47 13.9 (5.2) -6.10 [ -8.83, -3.37 ]

-50 -25 0 25 50


Analysis 1.4. Comparison 1 Rapid versus stepwise negative pressure application, Outcome 4 Apgar score <

7 after 1 minute.



Outcome: 4 Apgar score < 7 after 1 minute

Study or subgroup Favours rapid Stepwise application Risk Ratio Weight Risk Ratio

n/N n/N

M-H,Random,95%

CI

M-H,Random,95%

CI

Lim 1997 5/47 8/47 33.3 % 0.63 [ 0.22, 1.77 ]

Suwannachat 2011 24/330 18/330 66.7 % 1.33 [ 0.74, 2.41 ]

Total (95% CI) 377 377 100.0 % 1.04 [ 0.51, 2.09 ]

Total events: 29 (Favours rapid), 26 (Stepwise application)

Heterogeneity: Tau2 = 0.10; Chi2 = 1.54, df = 1 (P = 0.22); I2 =35%



0.1 0.2 0.5 1 2 5 10




Analysis 1.5. Comparison 1 Rapid versus stepwise negative pressure application, Outcome 5 Apgar score <

7 after 5 minutes.



Outcome: 5 Apgar score < 7 after 5 minutes



Lim 1997 1/47 1/47 20.0 % 1.00 [ 0.06, 15.52 ]

Suwannachat 2011 4/330 4/330 80.0 % 1.00 [ 0.25, 3.96 ]

Total (95% CI) 377 377 100.0 % 1.00 [ 0.29, 3.42 ]





0.005 0.1 1 10 200


Analysis 1.6. Comparison 1 Rapid versus stepwise negative pressure application, Outcome 6 Scalp

laceration > 1/4.



Outcome: 6 Scalp laceration > 1/4



Lim 1997 3/37 4/36 0.73 [ 0.18, 3.03 ]

0.1 0.2 0.5 1 2 5 10




Analysis 1.7. Comparison 1 Rapid versus stepwise negative pressure application, Outcome 7

Cephalhematoma.



Outcome: 7 Cephalhematoma


n/N n/N

M-H,Random,95%

CI

M-H,Random,95%

CI

Lim 1997 5/37 4/36 33.3 % 1.22 [ 0.35, 4.17 ]

Suwannachat 2011 11/330 22/330 66.7 % 0.50 [ 0.25, 1.01 ]

Total (95% CI) 367 366 100.0 % 0.67 [ 0.30, 1.53 ]


Heterogeneity: Tau2 = 0.13; Chi2 = 1.51, df = 1 (P = 0.22); I2 =34%



0.1 0.2 0.5 1 2 5 10


Analysis 1.8. Comparison 1 Rapid versus stepwise negative pressure application, Outcome 8 Subgaleal

hemorrhage.



Outcome: 8 Subgaleal hemorrhage



Suwannachat 2011 7/330 6/330 1.17 [ 0.40, 3.43 ]

0.02 0.1 1 10 50




Analysis 1.9. Comparison 1 Rapid versus stepwise negative pressure application, Outcome 9

Hyperbilirubinemia.



Outcome: 9 Hyperbilirubinemia



Suwannachat 2011 68/330 77/330 0.88 [ 0.66, 1.18 ]

0.2 0.5 1 2 5


Analysis 1.10. Comparison 1 Rapid versus stepwise negative pressure application, Outcome 10 Second

degree of perineal tears.



Outcome: 10 Second degree of perineal tears



Lim 1997 5/47 7/47 0.71 [ 0.24, 2.09 ]

0.1 0.2 0.5 1 2 5 10




Analysis 1.11. Comparison 1 Rapid versus stepwise negative pressure application, Outcome 11 Third

degree of perineal tears.



Outcome: 11 Third degree of perineal tears



Lim 1997 1/47 1/47 3.8 % 1.00 [ 0.06, 15.52 ]

Suwannachat 2011 34/330 25/330 96.2 % 1.36 [ 0.83, 2.23 ]

Total (95% CI) 377 377 100.0 % 1.35 [ 0.83, 2.19 ]





0.01 0.1 1 10 100


Analysis 1.12. Comparison 1 Rapid versus stepwise negative pressure application, Outcome 12 Umbilical

venous pH < 7.2.



Outcome: 12 Umbilical venous pH < 7.2



Lim 1997 2/47 1/47 2.00 [ 0.19, 21.31 ]

0.01 0.1 1 10 100




Analysis 1.13. Comparison 1 Rapid versus stepwise negative pressure application, Outcome 13 Number of

traction.



Outcome: 13 Number of traction

Study or subgroup Rapid application Stepwise applicationMean

DifferenceMean

Difference

N Mean(SD) N Mean(SD) IV,Fixed,95% CI IV,Fixed,95% CI

Lim 1997 47 2.9 (1.7) 47 2.8 (1.9) 0.10 [ -0.63, 0.83 ]

-10 -5 0 5 10


Analysis 1.14. Comparison 1 Rapid versus stepwise negative pressure application, Outcome 14 Perineal

pain after delivery.



Outcome: 14 Perineal pain after delivery



Suwannachat 2011 288/330 269/330 1.07 [ 1.00, 1.14 ]

0.5 0.7 1 1.5 2




Analysis 1.15. Comparison 1 Rapid versus stepwise negative pressure application, Outcome 15 Perineal

wound infection.



Outcome: 15 Perineal wound infection



Suwannachat 2011 1/330 2/330 0.50 [ 0.05, 5.49 ]

0.001 0.01 0.1 1 10 100 1000


Analysis 1.16. Comparison 1 Rapid versus stepwise negative pressure application, Outcome 16 Postpartum

hemorrhage.



Outcome: 16 Postpartum hemorrhage



Suwannachat 2011 12/330 20/330 0.60 [ 0.30, 1.21 ]

0.05 0.2 1 5 20




Analysis 1.17. Comparison 1 Rapid versus stepwise negative pressure application, Outcome 17 Perinatal

death.



Outcome: 17 Perinatal death



Suwannachat 2011 0/330 1/330 0.33 [ 0.01, 8.15 ]

0.001 0.01 0.1 1 10 100 1000


Analysis 1.18. Comparison 1 Rapid versus stepwise negative pressure application, Outcome 18 Obstetrician

satisfaction.



Outcome: 18 Obstetrician satisfaction



Suwannachat 2011 318/330 316/330 1.01 [ 0.98, 1.04 ]

0.5 0.7 1 1.5 2




Analysis 1.19. Comparison 1 Rapid versus stepwise negative pressure application, Outcome 19 Maternal

satisfaction.



Outcome: 19 Maternal satisfaction



Suwannachat 2011 325/330 325/330 1.00 [ 0.98, 1.02 ]

0.5 0.7 1 1.5 2


A P P E N D I C E S

Appendix 1. Methods to be used if other studies identified

We will use the mean difference to combine trials that measure the same outcome, but use different methods. If there is evidence of

skewness, this will be reported.

We will assess heterogeneity by visual forest plots of the outcomes’ data among trials and by using the I2 statistic (Higgins 2005) with

95% confidence interval. If we find statistical heterogeneity among the trials, inconsistent forest plots and an I2 exceeding 50%, we

will look for an explanation using subgroup analysis. The analysis will be conducted where sufficient data are available according to the

following specified factors including type of vacuum extraction procedure (ACOG 2000), type of cup, parity, gestation, indication of

delivery, with or without epidural anesthesia. If trials in individual subgroups of the potential factors are thought to be comparable by

interaction test as described by Deeks 2001, we will use a random-effects meta-analysis for estimating an overall summary. Alternatively,

we will use fixed-effect meta-analysis for combining data.

Where sufficient trials are included, we will consider publication bias using funnel plots of between-treatment effect and its precision

of individual trials, and Egger’s test (Egger 1997). If we find asymmetry funnel plots with statistical publication bias, we will further

examine the effect of the bias on the meta-analysis conclusion using sensitivity analysis.

We will carry out sensitivity analyses to explore the effect of trial quality and, where appropriate, cluster-randomized trials on the meta-

analysis conclusion. The trial quality will involve analysis based on high-quality trials. Trials of poor quality will be excluded in the

analysis (those rating B, C, or D) in order to assess for any substantive difference to the overall result.



Appendix 2. Methods used to assess trials included in previous versions of this review

Selection of studies

Two authors assessed for inclusion all potential studies we identified as a result of the search strategy. There were no disagreements.

Assessment of methodological quality of included studies

Two authors assessed the validity of the identified study using the criteria outlined in the Cochrane Handbook for Systematic Reviews ofInterventions (Higgins 2005). We have described the methods used for generation of the randomization sequence in the Characteristicsof included studies table.

(1) Selection bias (allocation concealment)

We assigned a quality score using the following criteria:

(A) adequate concealment of allocation: such as telephone randomization, consecutively-numbered, sealed opaque envelopes;

(B) unclear whether adequate concealment of allocation: such as list or table used, sealed envelopes or study does not report any

concealment approach;

(C) inadequate concealment of allocation: such as open list of random-number tables, use of case record numbers, dates of birth or

days of the week.

(2) Attrition bias (loss of participants, e.g. discharge very soon after birth, withdrawals, dropouts, protocol deviations)

We assessed completeness to follow-up using the following criteria:

(A) less than 5% loss of participants;

(B) 5% to 9.9% loss of participants;

(C) 10% to 19.9% loss of participants;

(D) more than 20% loss of participants.

(3) Detection bias (blinding of outcome assessment)

We assessed detection bias using the following criteria:

(A) adequate blinding explanation: such as investigators measured birth passage injury among the women without awareness of the

interventions they received;

(B) unclear blinding explanation: such as investigators measured birth passage injury among the women similarly;

(C) inadequate blinding explanation: such as birth passage injury was measured from the women in both groups.

The one identified and included trial scored an A when rating selection bias and detection bias.

Data extraction and management

We used the Cochrane Pregnancy and Childbirth Group’s data extraction form template to extract data. Two review authors extracted

the data using the agreed form. There were no discrepancies. We used the Review Manager software (RevMan 2003) to enter data.

Data analysis

We carried out statistical analysis using RevMan 2003. Where relevant, we reported birth passage injury, postpartum hemorrhage, birth

asphyxia, fetal injury and other binary outcomes using risk ratio with 95% confidence intervals.

If we had identified more than one trial or if we identify other trials in future updates, we will use the methods we prespecified in the

published protocol - see Appendix 1.



W H A T ’ S N E W

Last assessed as up-to-date: 8 May 2012.

Date Event Description

8 May 2012 New citation required and conclusions have changed Although the conclusions have not changed overall, the in-

clusion of data from a new study has reinforced them. Pre-

viously, due to a small number of participants in the single

included trial, the evidence to draw conclusions was limited

4 April 2012 New search has been performed Search updated. One new trial included (Suwannachat 2011)

.

H I S T O R Y

Protocol first published: Issue 3, 2007

Review first published: Issue 3, 2008

Date Event Description

29 April 2008 Amended Converted to new review format

C O N T R I B U T I O N S O F A U T H O R S

B Suwannachat (BS) initiated the topic. BS, P Lumbiganon and M Laopaiboon (ML) drafted the protocol. All review authors approved

the final version of the protocol.

BS drafted the first version of the review. All review authors approved the final version of the review.

BS and ML drafted the updated version of the review. All authors approved the final version of the updated review.

D E C L A R A T I O N S O F I N T E R E S T

B Suwannachat and M Laopaiboon are authors of one of the included studies (Suwannachat 2011). Data extraction and ’Risk of bias’

assessment were carried out by three independent assessors who were not involved in the study.



S O U R C E S O F S U P P O R T

Internal sources

• Kalasin Hospital, Ministry of Public Health, Thailand.

• Faculty of Medicine, Khon Kaen University, Thailand.

• Faculty of Public Health, Khon Kaen University, Thailand.

External sources

• Thailand Research Fund, Senior research scholar, Thailand.

• Thailand Cochrane Network, Thailand.

I N D E X T E R M S

Medical Subject Headings (MeSH)

Pressure; Randomized Controlled Trials as Topic; Vacuum Extraction, Obstetrical [∗methods]

MeSH check words

Female; Humans; Pregnancy



Rapidversusstepwisenegativepressureapplicationfor ... (rapid versus stepwise negative... ·...

Documents

Transcript of Rapidversusstepwisenegativepressureapplicationfor ... (rapid versus stepwise negative... ·...