Description of the condition
In 2010, 71.7% of Australian women sustained some degree of perineal (area between the vagina and anus) trauma during childbirth (Li 2012). Obstetric anal sphincter injuries (OASIS) include third and fourth degree tears, were detected in 1.8% of vaginal births (Li 2012), and are of particular concern as they are associated with high rates of short- and long-term consequences for the woman. Perineal damage can occur via a spontaneous tear or an episiotomy (cut made to assist childbirth), and is classified by the degree of trauma sustained. The following classification described by Sultan (Sultan 1999) has been adopted by the international consultation on incontinence (Norton 2002) and will be used in this review (RCOG 2007).
- First degree – injury to the perineal skin only.
- Second degree – injury to perineum involving perineal muscles but not involving the anal sphincter.
- Third degree – injury to perineum involving the anal sphincter complex:
- 3a – less than 50% of the external anal sphincter (EAS);
- 3b – more than 50% of the EAS;
- 3c – both the EAS and internal anal sphincter (IAS).
- Fourth degree – injury to perineum involving the anal sphincter complex (EAS and IAS) and anal epithelium.
Risk factors for perineal trauma
Women are at a higher risk of sustaining an OASIS if they have a forceps birth, are having their first baby, are in the second stage of labour for more than one hour, deliver a baby weighing more than 4 kg, have a midline episiotomy or if the baby is in a persistent occipitoposterior position (RCOG 2007).
Diagnosis of perineal trauma
Following vaginal birth all women are examined by the accoucher (person delivering baby) to assess the presence and degree of perineal trauma. This examination should include a PR (per rectum) examination to assess the extent of any sphincter/anal trauma. However, assessing these tears can often be difficult due to multiple factors (poor lighting, lack of pain relief and difficulty identifying anatomy) leading to a potential classification of OASIS as second degree perineal trauma. There is also a disincentive on behalf of accouchers to report such injuries as they are often the subject of clinical audits and peer review meetings within obstetric units (Andrews 2006).
A prospective cohort study (Andrews 2006) of 254 primiparous women showed that 25% sustained OASIS, of which 87% were missed by the midwives, 14% missed by specialist registrars and 67% missed by senior house officers. In this particular study 98.8% of these OASIS were subsequently detected on clinical examination by a trained research fellow prior to endoanal ultrasound (EAUS). Another prospective cohort study showed that 28% of the second degree tears actually had an occult (clinically undetected) third degree tear and that this was associated with an odds ratio of 8.8 of having anal incontinence at three months (Faltin 2000). Under-reporting and under-identification may lead to a suboptimal primary repair and increased rates of maternal morbidity.
Outcomes and complications of anal sphincter injury
OASIS is the most important aetiological factor in the pathogenesis of anal incontinence in women (Swash 1993). Anal incontinence is defined by the International Continence Society as involuntary loss of flatus or faeces (Haylen 2010) and affects up to 40% of women following childbirth (Faltin 2000). The embarrassing nature of this problem leads to social isolation and many women not seeking medical treatment for their symptoms (Fernando 2010).
With primary detection and appropriate repair, women can be reassured that the prognosis is good with 60% to 80% being asymptomatic at 12 months.(RCOG 2007). Possible complications after anal sphincter injury range from perineal pain, difficulty with emptying the bladder or bowels, faecal urgency, anal incontinence to long-term dyspareunia (painful sexual intercourse) and more rarely, rectovaginal fistulas (abnormal connection between vagina and rectum). However, there are also rates varying between 20% to 40% of occult OASIS injuries. It remains to be established whether these injuries are truly “occult” or represent “overt” anal sphincter injuries that have either been wrongly classified as a second degree tear or missed (Andrews 2006).
Description of the intervention
EAUS is a simple procedure that does not have any associated risks and is not painful. A probe inserted into the anus allows the practitioner to view the structures of the anal canal. EAUS has been shown to be equivalent to MRI (magnetic resonance imaging) and superior to electromyographic sphincter mapping in detecting sphincter defects (Felt-Bersma 2006), is much cheaper, and more easily accessible with bedside units suitable for use on the labour ward. Obstetricians and pregnant women are also familiar with ultrasound techniques as they are commonly used throughout pregnancy via transabdominal and transvaginal approaches, making the intervention potentially more acceptable to women.
How the intervention might work
EAUS performed prior to surgical repair of visible obstetric trauma could improve detection rates of OASIS and allow for improved surgical repair and by doing so, reduce the morbidity suffered by women undergoing vaginal birth. EAUS could also be used as part of the early follow-up of patients with OASIS to identify patients at higher risk of long-term complications. This would allow for early referral to specialist centres or a colorectal surgeon, and intervention with either physiotherapy and dietary manipulation or if needed, secondary sphincter repair (Fowler 2009).
EAUS may also be useful in pregnant women who have had a prior OASIS, to plan mode of delivery. Seventeen per cent to twenty-four per cent of women who underwent a vaginal delivery after OASIS had worsening of their faecal symptoms (RCOG 2007). However, a large prospective cohort study found that recurrence of OASIS could not be predicted and that 95% of women with a prior injury did not sustain further overt sphincter damage during a subsequent vaginal delivery (Harkin 2003). This raises the question as to whether antenatal evaluation with EAUS may help identify those patients at high risk of worsening symptoms so they could be offered an elective lower segment caesarean section (LSCS) to reduce these risks.
Why it is important to do this review
It is important to systematically review the evidence for using EAUS in the detection and management of primary OASIS, as such an intervention may decrease complications by directing more suitable treatment/surgical repair and improving physical symptoms and quality of life for women.
To evaluate the role of EAUS in:
- the detection of OASIS in the immediate postpartum period following vaginal birth;
- reducing the risk of associated maternal complications related to OASIS.
Criteria for considering studies for this review
Types of studies
We will include published and unpublished randomised controlled trials, cluster-randomised trials and studies presented only as abstracts. Trials using quasi-randomised trials and cross-over design will be excluded.
Types of participants
All women experiencing or who have previously had a vaginal birth at any gestation, including spontaneous and assisted vaginal births.
Types of interventions
- EAUS performed following vaginal birth and prior to repair of any perineal trauma.
- EAUS performed following vaginal birth after repair of any perineal trauma, including women undergoing EAUS during subsequent pregnancies.
Types of outcome measures
- Anal incontinence, defined as involuntary loss of flatus or faeces, which is a social or hygiene problem.
- Faecal incontinence (involuntary loss of solid stool) as specified by trialist.
- Flatal incontinence (involuntary loss of flatus) as specified by trialist.
- Anal incontinence, defined as involuntary loss of flatus or faeces, which is a social or hygiene problem measured at < three months, three to 12 months and > 12 months.
- Faecal urgency as specified by trialist.
- Detection of obstetric anal sphincter injuries (defined as interruption of the external anal sphincter, with or without damage to the internal anal sphincter or anal mucosa).
- Perineal pain, as assessed by a visual analogue scale at three months postpartum or as specified by trialists.
- Dyspareunia assessed by a visual analogue scale as specified by trialists.
- Need for secondary repair of external anal sphincter.
- Maternal quality of life as specified by trialist.
- Planned mode of birth in subsequent pregnancy.
- Actual mode of birth in subsequent pregnancy.
- Women's satisfaction with care.
Search methods for identification of studies
We will contact the Trials Search Co-ordinator to search the Cochrane Pregnancy and Childbirth Group’s Trials Register.
The Cochrane Pregnancy and Childbirth Group’s Trials Register is maintained by the Trials Search Co-ordinator and contains trials identified from:
- monthly searches of the Cochrane Central Register of Controlled Trials (CENTRAL);
- weekly searches of MEDLINE;
- weekly searches of Embase;
- handsearches of 30 journals and the proceedings of major conferences;
- 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 proceedings, and the list of journals reviewed via the current awareness 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.
Searching other resources
We plan to search reference lists of retrieved studies.
We will not apply any language restrictions.
Data collection and analysis
Selection of studies
Both review authors will independently assess for inclusion all the potential studies we identify as a result of the search strategy. We will resolve any disagreement through discussion or, if required, we will consult a third person.
Data extraction and management
We will design a form to extract data. For eligible studies, both review authors will extract the data using the agreed form. We will resolve discrepancies through discussion or, if required, we will consult a third person. We will enter data into Review Manager software (RevMan 2012) and check for accuracy.
When information regarding any of the above is unclear, we will attempt to contact authors of the original reports to provide further details.
Assessment of risk of bias in included studies
Both review authors will independently assess risk of bias for each study using the criteria outlined in the Cochrane Handbook for Systematic Reviews of Interventions (Higgins 2011). We will resolve any disagreement by discussion or by involving a third assessor.
(1) Random sequence generation (checking for possible selection bias)
We will describe 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 will assess 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 (checking for possible selection bias)
We will describe for each included study the method used to conceal allocation to interventions prior to assignment and will assess whether intervention allocation could have been foreseen in advance of, or during recruitment, or changed after assignment.
We will assess the methods as:
- low risk of bias (e.g. telephone or central randomisation; 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 will describe for each included study the methods used, if any, to blind study participants and personnel from knowledge of which intervention a participant received. We will consider that studies are at low risk of bias if they were blinded, or if we judge that the lack of blinding would be unlikely to affect results. We will assess blinding separately for different outcomes or classes of outcomes.
We will assess the methods as:
- low, high or unclear risk of bias for participants;
- low, high or unclear risk of bias for personnel.
(3.2) Blinding of outcome assessment (checking for possible detection bias)
We will describe for each included study the methods used, if any, to blind outcome assessors from knowledge of which intervention a participant received. We will assess blinding separately for different outcomes or classes of outcomes.
We will assess methods used to blind outcome assessment as:
- low, high or unclear risk of bias.
(4) Incomplete outcome data (checking for possible attrition bias due to the amount, nature and handling of incomplete outcome data)
We will describe for each included study, and for each outcome or class of outcomes, the completeness of data including attrition and exclusions from the analysis. We will state whether attrition and exclusions were reported and the numbers included in the analysis at each stage (compared with the total randomised participants), reasons for attrition or exclusion where reported, and whether missing data were balanced across groups or were related to outcomes. Where sufficient information is reported, or can be supplied by the trial authors, we will re-include missing data in the analyses which we undertake.
We will assess 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 randomisation);
- unclear risk of bias.
(5) Selective reporting (checking for reporting bias)
We will describe for each included study how we investigated the possibility of selective outcome reporting bias and what we found.
We will assess 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 (checking for bias due to problems not covered by (1) to (5) above)
We will describe for each included study any important concerns we have about other possible sources of bias.
We will assess whether each study was free of other problems that could put it at risk of bias:
- low risk of other bias;
- high risk of other bias;
- unclear whether there is risk of other bias.
(7) Overall risk of bias
We will make explicit judgements about whether studies are at high risk of bias, according to the criteria given in the Cochrane Handbook (Higgins 2011). With reference to (1) to (6) above, we will assess the likely magnitude and direction of the bias and whether we consider it is likely to impact on the findings. We will explore the impact of the level of bias through undertaking sensitivity analyses - see Sensitivity analysis.
Measures of treatment effect
For dichotomous data, we will present results as summary risk ratio with 95% confidence intervals.
For continuous data, we will use the mean difference if outcomes are measured in the same way between trials. We will use the standardised mean difference to combine trials that measure the same outcome, but use different methods.
Unit of analysis issues
We do not plan to include cluster or cross-over trials.
Dealing with missing data
For included studies, we will note levels of attrition. We will explore the impact of including studies with high levels of missing data in the overall assessment of treatment effect by using sensitivity analysis.
For all outcomes, we will carry out analyses, as far as possible, on an intention-to-treat basis, i.e. we will attempt to include all participants randomised to each group in the analyses, and all participants will be analysed in the group to which they were allocated, regardless of whether or not they received the allocated intervention. The denominator for each outcome in each trial will be the number randomised minus any participants whose outcomes are known to be missing.
Assessment of heterogeneity
We will assess statistical heterogeneity in each meta-analysis using the T², I² and Chi² statistics. We will regard heterogeneity as substantial if the I² is greater than 30% and either the T² is greater than zero, or there is a low P value (less than 0.10) in the Chi² test for heterogeneity.
Assessment of reporting biases
If there are 10 or more studies in the meta-analysis, we will investigate reporting biases (such as publication bias) using funnel plots. We will assess funnel plot asymmetry visually. If asymmetry is suggested by a visual assessment, we will perform exploratory analyses to investigate it.
We will carry out statistical analysis using the Review Manager software (RevMan 2012). We will use fixed-effect meta-analysis for combining data where it is reasonable to assume that studies are estimating the same underlying treatment effect: i.e. where trials are examining the same intervention, and the trials’ populations and methods are judged sufficiently similar. If there is clinical heterogeneity sufficient to expect that the underlying treatment effects differ between trials, or if substantial statistical heterogeneity is detected, we will use random-effects meta-analysis to produce an overall summary, if an average treatment effect across trials is considered clinically meaningful. The random-effects summary will be treated as the average range of possible treatment effects and we will discuss the clinical implications of treatment effects differing between trials. If the average treatment effect is not clinically meaningful, we will not combine trials.
If we use random-effects analyses, the results will be presented as the average treatment effect with 95% confidence intervals, and the estimates of T² and I².
Subgroup analysis and investigation of heterogeneity
If we identify substantial heterogeneity, we will investigate it using subgroup analyses and sensitivity analyses. We will consider whether an overall summary is meaningful, and if it is, use random-effects analysis to produce it.
We plan to carry out the following subgroup analyses.
- Women following their first vaginal birth versus women who have had multiple vaginal births.
- Assisted versus spontaneous vaginal birth.
The following outcome will be used in subgroup analysis: rates of anal incontinence.
We will assess subgroup differences by interaction tests available within RevMan (RevMan 2012). We will report the results of subgroup analyses quoting the χ² statistic and P value, and the interaction test I² value.
We plan to carry out sensitivity analyses to explore the effects of trial quality as assessed by concealment of allocation or missing data for a particular outcome on the summary statistic. We plan to exclude trials with greater than 20% missing data. We plan to exclude studies of poor quality from the analysis in order to assess for any substantive difference to the overall result. If no substantive difference exists, we plan to leave the studies in.
As part of the pre-publication editorial process, this protocol has been commented on by four peers (an editor and three referees who are external to the editorial team) and the Group's Statistical Adviser.
The National Institute for Health Research (NIHR) is the largest single funder of the Cochrane Pregnancy and Childbirth Group. The views and opinions expressed therein are those of the authors and do not necessarily reflect those of the NIHR, NHS or the Department of Health.
Contributions of authors
Kate Walsh acts as the guarantor, co-ordinating the review. Rosalie Grivell provided advice on clinical and methodological aspects of the protocol.
Declarations of interest