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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
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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)
Copyright © 2012 The Cochrane Collaboration. Published by John Wiley & Sons, Ltd.
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[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.
Copyright © 2012 The Cochrane Collaboration. Published by John Wiley & Sons, Ltd.
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)
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mailto:[email protected]
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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-
2Rapid versus stepwise negative pressure application for vacuum extraction assisted vaginal delivery (Review)
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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.
3Rapid versus stepwise negative pressure application for vacuum extraction assisted vaginal delivery (Review)
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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);
• unclear risk of bias.
(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);
• unclear risk of bias.
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(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);
• unclear risk of bias.
(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.
5Rapid versus stepwise negative pressure application for vacuum extraction assisted vaginal delivery (Review)
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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.
6Rapid versus stepwise negative pressure application for vacuum extraction assisted vaginal delivery (Review)
Copyright © 2012 The Cochrane Collaboration. Published by John Wiley & Sons, Ltd.
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Figure 1. ’Risk of bias’ graph: review authors’ judgements about each risk of bias item presented as
percentages across all included studies.
7Rapid versus stepwise negative pressure application for vacuum extraction assisted vaginal delivery (Review)
Copyright © 2012 The Cochrane Collaboration. Published by John Wiley & Sons, Ltd.
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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.
8Rapid versus stepwise negative pressure application for vacuum extraction assisted vaginal delivery (Review)
Copyright © 2012 The Cochrane Collaboration. Published by John Wiley & Sons, Ltd.
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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.
9Rapid versus stepwise negative pressure application for vacuum extraction assisted vaginal delivery (Review)
Copyright © 2012 The Cochrane Collaboration. Published by John Wiley & Sons, Ltd.
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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.
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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
of Systematic Reviews 2010, Issue 11. [DOI: 10.1002/
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
of Systematic Reviews 2008, Issue 3. [DOI: 10.1002/
14651858.CD006636.pub2]∗ Indicates the major publication for the study
11Rapid versus stepwise negative pressure application for vacuum extraction assisted vaginal delivery (Review)
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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
12Rapid versus stepwise negative pressure application for vacuum extraction assisted vaginal delivery (Review)
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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
13Rapid versus stepwise negative pressure application for vacuum extraction assisted vaginal delivery (Review)
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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
14Rapid versus stepwise negative pressure application for vacuum extraction assisted vaginal delivery (Review)
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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.
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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
16Rapid versus stepwise negative pressure application for vacuum extraction assisted vaginal delivery (Review)
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Analysis 1.2. Comparison 1 Rapid versus stepwise negative pressure application, Outcome 2 Detachment
rate.
Review: Rapid versus stepwise negative pressure application for vacuum extraction assisted vaginal delivery
Comparison: 1 Rapid versus stepwise negative pressure application
Outcome: 2 Detachment rate
Study or subgroup Rapid application Stepwise application Risk Ratio Weight Risk Ratio
n/N n/N M-H,Fixed,95% CI M-H,Fixed,95% CI
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
17Rapid versus stepwise negative pressure application for vacuum extraction assisted vaginal delivery (Review)
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Analysis 1.3. Comparison 1 Rapid versus stepwise negative pressure application, Outcome 3 Duration of
vacuum extraction procedure.
Review: Rapid versus stepwise negative pressure application for vacuum extraction assisted vaginal delivery
Comparison: 1 Rapid versus stepwise negative pressure application
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
Favours rapid Favours stepwise
Analysis 1.4. Comparison 1 Rapid versus stepwise negative pressure application, Outcome 4 Apgar score <
7 after 1 minute.
Review: Rapid versus stepwise negative pressure application for vacuum extraction assisted vaginal delivery
Comparison: 1 Rapid versus stepwise negative pressure application
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%
Test for overall effect: Z = 0.10 (P = 0.92)
Test for subgroup differences: Not applicable
0.1 0.2 0.5 1 2 5 10
Favours rapid Favours stepwise
18Rapid versus stepwise negative pressure application for vacuum extraction assisted vaginal delivery (Review)
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Analysis 1.5. Comparison 1 Rapid versus stepwise negative pressure application, Outcome 5 Apgar score <
7 after 5 minutes.
Review: Rapid versus stepwise negative pressure application for vacuum extraction assisted vaginal delivery
Comparison: 1 Rapid versus stepwise negative pressure application
Outcome: 5 Apgar score < 7 after 5 minutes
Study or subgroup Rapid application Stepwise application Risk Ratio Weight Risk Ratio
n/N n/N M-H,Fixed,95% CI M-H,Fixed,95% CI
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 ]
Total events: 5 (Rapid application), 5 (Stepwise application)
Heterogeneity: Chi2 = 0.0, df = 1 (P = 1.00); I2 =0.0%
Test for overall effect: Z = 0.0 (P = 1.0)
Test for subgroup differences: Not applicable
0.005 0.1 1 10 200
Favours rapid Favours stepwise
Analysis 1.6. Comparison 1 Rapid versus stepwise negative pressure application, Outcome 6 Scalp
laceration > 1/4.
Review: Rapid versus stepwise negative pressure application for vacuum extraction assisted vaginal delivery
Comparison: 1 Rapid versus stepwise negative pressure application
Outcome: 6 Scalp laceration > 1/4
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
Lim 1997 3/37 4/36 0.73 [ 0.18, 3.03 ]
0.1 0.2 0.5 1 2 5 10
Favours rapid Favours stepwise
19Rapid versus stepwise negative pressure application for vacuum extraction assisted vaginal delivery (Review)
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Analysis 1.7. Comparison 1 Rapid versus stepwise negative pressure application, Outcome 7
Cephalhematoma.
Review: Rapid versus stepwise negative pressure application for vacuum extraction assisted vaginal delivery
Comparison: 1 Rapid versus stepwise negative pressure application
Outcome: 7 Cephalhematoma
Study or subgroup Rapid application Stepwise application Risk Ratio Weight Risk Ratio
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 ]
Total events: 16 (Rapid application), 26 (Stepwise application)
Heterogeneity: Tau2 = 0.13; Chi2 = 1.51, df = 1 (P = 0.22); I2 =34%
Test for overall effect: Z = 0.95 (P = 0.34)
Test for subgroup differences: Not applicable
0.1 0.2 0.5 1 2 5 10
Favours rapid Favours stepwise
Analysis 1.8. Comparison 1 Rapid versus stepwise negative pressure application, Outcome 8 Subgaleal
hemorrhage.
Review: Rapid versus stepwise negative pressure application for vacuum extraction assisted vaginal delivery
Comparison: 1 Rapid versus stepwise negative pressure application
Outcome: 8 Subgaleal hemorrhage
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 7/330 6/330 1.17 [ 0.40, 3.43 ]
0.02 0.1 1 10 50
Favours rapid Favours stepwise
20Rapid versus stepwise negative pressure application for vacuum extraction assisted vaginal delivery (Review)
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Analysis 1.9. Comparison 1 Rapid versus stepwise negative pressure application, Outcome 9
Hyperbilirubinemia.
Review: Rapid versus stepwise negative pressure application for vacuum extraction assisted vaginal delivery
Comparison: 1 Rapid versus stepwise negative pressure application
Outcome: 9 Hyperbilirubinemia
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 68/330 77/330 0.88 [ 0.66, 1.18 ]
0.2 0.5 1 2 5
Favours rapid Favours stepwise
Analysis 1.10. Comparison 1 Rapid versus stepwise negative pressure application, Outcome 10 Second
degree of perineal tears.
Review: Rapid versus stepwise negative pressure application for vacuum extraction assisted vaginal delivery
Comparison: 1 Rapid versus stepwise negative pressure application
Outcome: 10 Second degree of perineal tears
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
Lim 1997 5/47 7/47 0.71 [ 0.24, 2.09 ]
0.1 0.2 0.5 1 2 5 10
Favours rapid Favours stepwise
21Rapid versus stepwise negative pressure application for vacuum extraction assisted vaginal delivery (Review)
Copyright © 2012 The Cochrane Collaboration. Published by John Wiley & Sons, Ltd.
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Analysis 1.11. Comparison 1 Rapid versus stepwise negative pressure application, Outcome 11 Third
degree of perineal tears.
Review: Rapid versus stepwise negative pressure application for vacuum extraction assisted vaginal delivery
Comparison: 1 Rapid versus stepwise negative pressure application
Outcome: 11 Third degree of perineal tears
Study or subgroup Rapid application Stepwise application Risk Ratio Weight Risk Ratio
n/N n/N M-H,Fixed,95% CI M-H,Fixed,95% CI
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 ]
Total events: 35 (Rapid application), 26 (Stepwise application)
Heterogeneity: Chi2 = 0.05, df = 1 (P = 0.83); I2 =0.0%
Test for overall effect: Z = 1.20 (P = 0.23)
Test for subgroup differences: Not applicable
0.01 0.1 1 10 100
Favours rapid Favours stepwise
Analysis 1.12. Comparison 1 Rapid versus stepwise negative pressure application, Outcome 12 Umbilical
venous pH < 7.2.
Review: Rapid versus stepwise negative pressure application for vacuum extraction assisted vaginal delivery
Comparison: 1 Rapid versus stepwise negative pressure application
Outcome: 12 Umbilical venous pH < 7.2
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
Lim 1997 2/47 1/47 2.00 [ 0.19, 21.31 ]
0.01 0.1 1 10 100
Favours rapid Favours stepwise
22Rapid versus stepwise negative pressure application for vacuum extraction assisted vaginal delivery (Review)
Copyright © 2012 The Cochrane Collaboration. Published by John Wiley & Sons, Ltd.
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Analysis 1.13. Comparison 1 Rapid versus stepwise negative pressure application, Outcome 13 Number of
traction.
Review: Rapid versus stepwise negative pressure application for vacuum extraction assisted vaginal delivery
Comparison: 1 Rapid versus stepwise negative pressure application
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
Favours rapid Favours stepwise
Analysis 1.14. Comparison 1 Rapid versus stepwise negative pressure application, Outcome 14 Perineal
pain after delivery.
Review: Rapid versus stepwise negative pressure application for vacuum extraction assisted vaginal delivery
Comparison: 1 Rapid versus stepwise negative pressure application
Outcome: 14 Perineal pain after delivery
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 288/330 269/330 1.07 [ 1.00, 1.14 ]
0.5 0.7 1 1.5 2
Favours rapid Favours stepwise
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Analysis 1.15. Comparison 1 Rapid versus stepwise negative pressure application, Outcome 15 Perineal
wound infection.
Review: Rapid versus stepwise negative pressure application for vacuum extraction assisted vaginal delivery
Comparison: 1 Rapid versus stepwise negative pressure application
Outcome: 15 Perineal wound infection
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 1/330 2/330 0.50 [ 0.05, 5.49 ]
0.001 0.01 0.1 1 10 100 1000
Favours rapid Favours stepwise
Analysis 1.16. Comparison 1 Rapid versus stepwise negative pressure application, Outcome 16 Postpartum
hemorrhage.
Review: Rapid versus stepwise negative pressure application for vacuum extraction assisted vaginal delivery
Comparison: 1 Rapid versus stepwise negative pressure application
Outcome: 16 Postpartum hemorrhage
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 12/330 20/330 0.60 [ 0.30, 1.21 ]
0.05 0.2 1 5 20
Favours rapid Favours stepwise
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Analysis 1.17. Comparison 1 Rapid versus stepwise negative pressure application, Outcome 17 Perinatal
death.
Review: Rapid versus stepwise negative pressure application for vacuum extraction assisted vaginal delivery
Comparison: 1 Rapid versus stepwise negative pressure application
Outcome: 17 Perinatal death
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 0/330 1/330 0.33 [ 0.01, 8.15 ]
0.001 0.01 0.1 1 10 100 1000
Favours rapid Favours stepwise
Analysis 1.18. Comparison 1 Rapid versus stepwise negative pressure application, Outcome 18 Obstetrician
satisfaction.
Review: Rapid versus stepwise negative pressure application for vacuum extraction assisted vaginal delivery
Comparison: 1 Rapid versus stepwise negative pressure application
Outcome: 18 Obstetrician satisfaction
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 318/330 316/330 1.01 [ 0.98, 1.04 ]
0.5 0.7 1 1.5 2
Favours stepwise Favours rapid
25Rapid versus stepwise negative pressure application for vacuum extraction assisted vaginal delivery (Review)
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Analysis 1.19. Comparison 1 Rapid versus stepwise negative pressure application, Outcome 19 Maternal
satisfaction.
Review: Rapid versus stepwise negative pressure application for vacuum extraction assisted vaginal delivery
Comparison: 1 Rapid versus stepwise negative pressure application
Outcome: 19 Maternal satisfaction
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 325/330 325/330 1.00 [ 0.98, 1.02 ]
0.5 0.7 1 1.5 2
Favours stepwise Favours rapid
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.
26Rapid versus stepwise negative pressure application for vacuum extraction assisted vaginal delivery (Review)
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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.
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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.
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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
29Rapid versus stepwise negative pressure application for vacuum extraction assisted vaginal delivery (Review)
Copyright © 2012 The Cochrane Collaboration. Published by John Wiley & Sons, Ltd.