Does the mode of delivery predispose women to anal incontinence in the first year postpartum? A comparative systematic review

Introduction 

Anal incontinence is a distressing and disabling symptom affecting 4.3% (95% CI 3.5–5.9) women aged 15–60 years.¹ It is increasingly acknowledged that childbirth is a risk factor for anal incontinence and that anal incontinence is an under- reported and under recognised symptom² that has a negative impact on quality of life.³ 

There are different definitions for anal incontinence. The Royal College of Physicians suggests ‘the involuntary or inap- propriate passage of faeces’.⁴ While this definition is clear, it makes no mention of urgency or flatus incontinence nor does it address the effect that the symptoms may have on the woman. This definition is refined by the International Con- tinence Society to read ‘Anal incontinence is the involuntary loss of flatus, liquid or solid stool that is a social or hygienic problem’.⁵ This definition has the advantages of not only including incontinence of flatus but also acknowledging that different women may react in very different ways to what appear to be the same symptoms. 

There has long been concern that vaginal delivery affects both urinary and anal continence, with some advocating cae- sarean section to protect the pelvic floor and anal continence mechanism. The correct identification⁶ and repair of tears involving the anal sphincter⁷ have been highlighted as ways of reducing the morbidity associated with anal incontinence. While these approaches have merit, avoidance of risk factors may reduce morbidity further. If the obstetric factors associ- ated with postpartum anal incontinence can be identified reliably, this knowledge has the potential to be translated into development of prevention strategies and may help inform the design of future studies. Accurate data on the risks and benefits of vaginal delivery and caesarean section will also inform both patients and clinicians when obtaining consent.

Wide variation exists in the available literature as to the significant aetiological factors with many studies being small and underpowered, leading to risk of an inability to detect an association when one exists. A number of studies exist but with conflicting results. No relevant systematic reviews of postpartum anal incontinence has been performed, and a comprehensive systematic review of the current evidence is required.

Methods

We developed a protocol using widely recommended methods for systematic reviews of observational studies for this study. The QUOROM statement8 and guidelines were followed during the preparation of this review (Appendix S2).

Identification of studies

Search and study selection The search focused on capturing studies in which the rates of anal incontinence in the first year postpartum according to the mode of delivery were reported. A search strategy was developed based on existing advice for observational studies.9,10 Medline (1984 to October 2004) and Embase (1984 to October 2004) and the Cochrane library (2003:3) were searched electronically. Papers from the past 20 years were chosen, as changes in the management of labour would make the findings from studies before this irrelevant. The search of Medline and Embase captured citations combining relevant MeSH, keywords and word variants for the concept ‘anal incontinence and childbirth’ (Appendix S1). In addition, bibliographies of relevant articles were manually searched, and experts in the specialty were contacted to identify papers not captured by electronic searches. The search was restricted to papers in the English language literature; however, this only excluded a small number of studies.11–15 Studies were selected in a two-stage process. First, all abstracts or titles in the electronic searches were scrutinised (S.J.P.), and full manuscripts of potentially eligible citations were obtained. Second, studies meeting our predefined criteria were selected. Studies were selected if data on anal incontinence could be extracted for participants following childbirth. Observational studies where individuals had reported their symptoms, either using a questionnaire or by interview, and sufficient data were provided to compute 2 · 2 tables were selected.

Studies without control groups were excluded as these do not help assess for aetiology as there is no comparative group. Where studies reported an odds ratio but no prevalence data was given, the results have been included in the data tables but not entered into the meta-analysis. Similarly, studies with a nonrepresentative control group are also included in the data tables but not entered into the meta-analysis. Studies with follow-up data which commenced less than 6 week or more than one year from the index delivery were excluded. Where more than one set of data was available for a cohort of women, the longest follow-up data less than 1 year was used. Studies that described singleton cephalic deliveries only were included and those relating to symptoms following multiple gestations or breech delivery were excluded.

Data extraction and study quality assessment Data were extracted using a piloted form on participants’ characteristics, study quality and anal incontinence rates. The quality10,16 of all selected papers was assessed for the following attributes: prospective continence assessment, prospective recruitment of population, adequate sampling of the selected population, method of ascertainment of risk factor, use of a validated measurement tool, temporality of the association and controls for confounding. Study design was examined to determine if continence assessment had been performed prospectively as the use of a continence diary would minimise recall bias. In aetiology studies, the participants selected should ideally be a representative cohort of postnatal women. Sampling was considered adequate if recruitment of participants was random or consecutive rather than performed for convenience. Another quality item was sought if the measurement tool to ascertain incontinence was developed rigorously17 and had been validated to ensure that patient responses were representative of disease. Ideally, studies should demonstrate the temporality of the association by only including those with new anal incontinence following

childbirth. Temporality of the association was also assessed as a quality item.

Our definition of anal incontinence included involuntary loss of solid or liquid faeces or flatus. Information was extracted on whether studies evaluated solid, liquid and flatus incontinence or faecal urgency in isolation or in combination. In some studies, the existence of multiple symptoms among individuals could not be evaluated separately due to the structure of the questionnaire used and the manner of reporting. Where possible, we computed odds ratios for isolated and combined symptoms. Thus, all studies initially included did not contribute to the quantitative data synthesis for each of the three incontinence symptoms.

Data synthesis Information from each study, stratified by mode of delivery was tabulated by symptoms. Data in individual studies were expressed as the odds ratio with 95% CI. Heterogeneity in rates was examined graphically and statistically. For graphical assessment, ‘forest’ plots of point estimates of rates and their 95% CIs were used. A random effects model18 was used in the light of heterogeneity.

We combined results for meta-analysis wherever appropriate in Review Manager 4.2.

Results

The electronic search yielded a total of 300 citations (Figure 1). On examination of titles and abstracts, 60 were found to be relevant to the review, and full papers were obtained for these. The reference lists of these revealed two further papers, and contact with experts revealed one further paper. No relevant systematic reviews was identified. Eighteen studies19–37 with 12 237 participants met the inclusion criteria, of which seventeen (94%) were from the past 10 years. Study characteristics are shown in (Table 1). Study quality assessment (Figure 2, Table 2) revealed deficiencies in many

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areas of methodology. None of the studies met all six highquality criteria. One study26 met five out of six criteria, and a further four studies met four criteria, but the remainder met three or less. Studies were not excluded for failure to meet quality criteria

Women having any type of vaginal delivery compared with a caesarean section had an increased risk of developing symptoms of solid, liquid or flatus anal incontinence. The risk varies with the mode of delivery ranging from a doubled risk with a forceps delivery (OR 2.01, 95% CI 1.47–2.74, P < 0.0001) to a third increased risk for a spontaneous vaginal delivery (OR 1.32, 95% CI 1.04–1.68, P = 0.02)

Instrumental deliveries also resulted in more symptoms of anal incontinence compared with spontaneous vaginal delivery (OR 1.47, 95% CI 1.22–1.78). This was statistically significant for forceps deliveries alone (OR 1.5, 95% CI 1.19 to1.89, P = 0.0006) but not for ventouse deliveries (OR 1.31, 95% CI 0.97–1.77, P = 0.08).

When studies examining severe symptoms of anal incontinence such as solid or liquid anal incontinence were analysed, although there was a trend towards more symptoms with vaginal delivery compared with caesarean section, this did not reach statistical significance. Only instrumental delivery compared with spontaneous vaginal delivery reached statistical significance for increased symptoms of solid and liquid anal incontinence (OR 1.91, 95% CI 1.00–3.67, P = 0.05).

Similarly, when comparing forceps and ventouse deliveries, when symptoms of flatus incontinence are included, forceps caused significantly more symptoms (OR 1.51, 95% CI 1.07– 2.13, P = 0.02), but this difference between the instruments disappeared when analysed for solid and liquid anal incontinence alone (OR 1.63, 95% CI 0.26 to10.02, P = 0.06).

The results are displayed graphically in (Figure 3) and tabulated in (Tables 3 and 4).

Discussion

This is the first systematic review of the obstetric factors associated with the occurrence of symptoms of anal incontinence in the first year postpartum. The mode of delivery appeared to influence the occurrence of symptoms of anal incontinence in the first year postpartum. However, the results are only statistically significant when incontinence of flatus is included in the analysis. When symptoms of solid and liquid anal incontinence are analysed alone, although there appears to be a trend towards increased symptoms with vaginal delivery compared with caesarean section, and with forceps or ventouse when compared with spontaneous vaginal delivery, this does not reach statistical significance.

The validity of the findings of this review is dependent on the rigor of its methodology.9 A prospective protocol was used and a concerted effort was made to identify all the available evidence in English. It met quality criteria laid down in

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the Meta-analysis of Observational Studies in Epidemiology statement.9 Additionally, continence data following delivery were available for 12 237 women, making this a very large cohort. Hence, this systematic review provides the most reliable evidence available on symptoms of anal incontinence according to mode to delivery in the first year postpartum

The methodological quality of the included studies was poor. The studies were heterogeneous with variation in follow-up intervals, differing definitions for anal incontinence, variable inclusion of women with and without clinical sphincter disruption and inconsistencies in controlling/discussion of predelivery continence. Nonstandard measurement tools were used to record outcome, and this may have introduced bias.

A further potential source of bias were studies that recruited women following delivery as women at higher risk of anal incontinence may have been preferentially encouraged to enter the study. In 7 of the 18 studies (39%), women were recruited following delivery. In the symptom category of solid, liquid or flatus incontinence, six of the seven studies recruited women following delivery, with only 130 women from 7791 (1.67%) selected antenatally, regardless of delivery factors .

This systematic review provides compelling evidence of an association between mode of delivery and anal incontinence, but this does not necessarily confirm cause and effect. Mode of delivery may be a surrogate marker for other factors such as long labour or increased infant birthweight. The data gained from this systematic review need to be interpreted with care in

the clinical situation. There is currently insufficient evidence to advocate caesarean section for reduction in major symptoms of incontinence in women without antenatal symptoms of anal incontinence.

Elucidating risk factors associated with postpartum anal incontinence enable development of studies that determine causation. In unravelling the aetiology of childbirth-related anal incontinence, studies need to be able to differentiate between pre-existing factors, which predispose women to anal incontinence and factors that occur at delivery, whether neurological39 or mechanical.7

Supplementary material

The following supplementary materials are available for this article:

Appendix S1. Search strategy for Chapter 2 using Ovid to search Medline and Embase.

Appendix S2. The QUOROM statement checklist.

These materials are available as part of the online article from: http://www.blackwell-synergy.com/doi/abs/10.1111/j.1471-0528. 2007.01553.x.

(This link will take you to the article abstract). Please note: Blackwell Publishing are not responsible for the content or functionality of any supplementary materials supplied by the authors. Any queries (other than missing material) should be directed to the corresponding author for the article.

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