Discussion
Main findings
Preventative value of CS for AI after
OASI
This analysis does not demonstrate a protective benefit for routine
elective CS in preventing new or worsening symptoms of AI after OASI in
a group of women who are both symptomatic and asymptomatic after their
index OASI. This was analysed from either a deterioration on a validated
scoring system or a description of new or worsening symptoms in women by
study authors after a subsequent birth after OASI. There is no evidence
of difference in deterioration of AI between women who deliver by CS
compared to women who deliver by VB after OASI overall, in the
shorter-term or longer-term (Figure 3A-C). For two studies in which an
asymptomatic group was analysed, there was also no evidence of a
difference in AI symptoms in the short-term; however there are
significant limitations to both studies (Figure 3D).
Regarding the certainty of the results, all included studies were at
high risk of bias for at least one outcome (Figure 1). This was due to:
limitations with the population recruited; non-randomisation to
treatment outcomes; inclusion of symptomatic women causing systemic
bias; retrospective analysis; failure to analyse by intention-to-treat
(emergency CS group included with elective CS group or excluded) and a
lack of validated outcome data measurement (Figure 2). We do not have
data to counsel specific groups; i.e. symptomatic women, asymptomatic
women, women with recurrent OASI.
Long term data
In the longer term, there is evidence from a larger population-based
study that women subsequently delivering by VB after OASI may experience
worsening of AI symptoms 5-12y after subsequent birth compared to CS;
however, this was not significant on the author’s multivariate analysis
(12). The study relied on retrospective recall of patient symptoms after
index birth. EAUS and ARMS were not used to routinely counsel women
regarding subsequent birth; it was national practice for symptomatic
women to undergo CS and asymptomatic women to undergo subsequent VB.
The other study providing long-term data outcomes compared two different
control groups of 50 patients however this study was not powered to
investigate long term AI symptoms between these groups (27). Therefore,
both studies in our meta-analysis have significant limitations and we
need higher quality data to investigate differences in long-term AI
symptoms in asymptomatic women after OASI who deliver by VB or CS.
Recurrence of OASI
Women who sustain an OASI recurrence have poorer long term incontinence
outcomes than women who deliver without an OASI (5); studies included in
this review did not provide data for this specific outcome. Rates of
index OASI are higher in teaching and university hospitals compared to
population-based studies and district-general hospitals (DGHs). However,
rates of recurrent OASI are highest in DGHs. There is an extremely wide
variation in OASI recurrence rates reported across studies, representing
a 25-fold difference. This may relate to training in OASI detection and
participation in research in some units, differences in OASI detection
rates and classification over time, regional differences in obstetric
practice and care to avoid recurrence e.g. by using OASI care bundles in
some units.
Strengths and limitations
This comprehensive review summarises the current evidence for whether
elective cesarean section is protective against the development of AI
after OASI. It uses a robust prospectively published systematic
methodology to double-extract data and appraise the risk of bias of this
data by two independent study authors. This is an extremely important
area clinically as AI has a profound negative effect on the lives of
young women, OASI is common, and AI is very common after OASI. This area
is under-researched; current guidelines utilise level 4 evidence and
there is consequently widespread variation in clinical practice.
This study meta-analyses both (1) the total incidence of AI after
subsequent VB compared to subsequent CS after OASI and (2) the presence
of new or worsening AI after subsequent VB compared to subsequent CS
after OASI. To our knowledge, it is the first study to investigate both
outcomes. It highlights challenges appraising evidence from
non-randomised mode of birth studies due to significant confounding
caused by including women with pre-existing symptoms of AI. It is
therefore difficult to provide clinically interpretable information on
the preventative value of CS against worsening AI from existing
published data.
Asymptomatic vs symptomatic
women
This review is limited by the methodology of the published data,
particularly the ability to extract values for just women who are
symptomatic or asymptomatic after index OASI. When counselling women
clinically, this is an important factor. Most studies are service
evaluations which include both symptomatic and asymptomatic women as one
group. Additionally, most published data do not used a validated
incontinence score to pair data pre- and post- birth after OASI
therefore it is difficult to extract data for women who have ‘new’ or
‘worse’ AI after birth.
Quality of the data
The vast majority of included studies were at high risk of bias for at
least one outcome. This was due to: limitations with the population
recruited; non-randomisation to treatment outcomes; inclusion of
symptomatic women causing systemic bias; retrospective analysis; failure
to analyse by intention-to-treat (emergency cesarean group included with
elective cesarean group or excluded); and a lack of validated outcome
data assessment (Figure 1). All studies except two included women with
pre-existing AI symptoms.
Data heterogeneity
One difference between studies is the use of EAUS, ARMS and 3D-TPUS to
assess anal sphincter defects and counsel women alongside symptoms to
undergo planned VB or planned CS after OASI (Table S1, S4). Defects on
EAUS are significantly correlated with symptoms of AI both in women with
a history of OASI diagnosed at birth (55% have a persistent sphincter
defect and 38% have AI) and in those without (13% have sphincter
defects and 14% have AI) (83). We include all women in these
meta-analyses however it would be valuable to appreciate the role of
EAUS, ARMs and 3D-TPUS in the long term in guiding practice,
specifically whether CS is valuable in preventing AI in asymptomatic
women with defects/abnormal physiology who undergo subsequent birth.
Deviations from study
protocol
Although our protocol aim was to stratify AI by follow up time period
(short-term (≤1y), medium-term (>1y <5y),
long-term (≥5y)) this was not due to the ranges in follow-up time period
employed by particular studies (S4) (12, 31, 33, 34). Instead, we
meta-analyses two time periods; 3-24 months (short term) and ≥5y (long
term).
Interpretation of results
This systematic review has not demonstrated a protective effect of CS
over VB to prevent new or worsening AI symptoms after OASI in the
short-term. Data presented in this meta-analysis represents a mixed
group of symptomatic and asymptomatic women and nearly all studies were
at high risk of bias and short follow up duration. It therefore does not
reliably assess an effect of subsequent MOB on long-term AI outcomes, or
provide individualised risk assessment for groups of women who are
symptomatic or asymptomatic after OASI.
Evidence to support counselling women after OASI is limited. There is a
paucity of data on long-term outcomes and knowledge about women’s
preferences and decision-making (84). Factors predicting worse AI with
subsequent birth after OASI include transient or ongoing AI symptoms
after index birth (13), fourth-degree tear (5, 24) and recurrent OASI
(4). Factors predicting better AI outcomes with subsequent birth after
OASI include absence of AI after index birth (13), normal anorectal
physiology (29), lesser degree of injury (24) and absence of injury at
subsequent birth (4).
Practical and research
recommendations
The evidence included in this review is limited and comes mostly from
service evaluations undertaken on mixed groups of women (17, 18, 19, 29,
31, 32, 70, 82). Higher-quality evidence is required to enable
clinicians to personalise the risk of future AI based on index birth
factors, maternal risk and current pregnancy details in women who
deliver after OASI. This should differentiate the risk for asymptomatic
and symptomatic women. Research to ascertain the value of anorectal
physiology investigations in predicting longer term AI outcomes would be
beneficial and enable standardisation of antenatal counselling pathways.