Effect of subsequent vaginal delivery on bowel symptoms and anorectal function in women who sustained a previous obstetric anal sphincter injury

In this prospective study of women who sustained OASIs, we found no significant worsening of anorectal symptoms, sphincter function and sphincter integrity when recommendation for subsequent mode of delivery was based upon a comprehensive antenatal assessment comprising SMIS, anal manometry and EAUS. When analysing sphincter function, a significantly lower postpartum squeeze pressure was noted in the VD group, a trend that was also observed in the subgroup of symptomatic women with normal anorectal physiology. This is perhaps an unsurprising finding in the immediate postpartum period following VD and may be a transient state that is part of normal postpartum physiology. Indeed, a previous study assessing the effect of pregnancy and childbirth on pelvic floor muscle function reported worsening squeeze pressures at 14 weeks postpartum, which had recovered completely by 1 year postpartum [17].

Although overall anorectal symptoms for the whole cohort remained unchanged following VD and CS, improvements in the CS group were noted in quality of life (p = 0.011) and symptoms of faecal urgency (p = 0.026) at 3 months postpartum. This is likely to be attributable to the effect of pregnancy exacerbating symptoms of faecal incontinence in women with established symptoms, with a return to baseline following delivery. An increase in urgency symptoms was also seen in the VD subgroup, and it is perhaps unsurprising that women who were symptomatic before delivery may experience some worsening of symptoms in the immediate postpartum period, a phenomenon that is likely to recover with time as can be seen with squeeze pressure [17]. A study with greater numbers and longer-term follow-up is needed to be able to comment on the significance of this finding, but our initial results are encouraging and suggest that if our triage criteria are followed, symptomatic women with normal physiology could have a VD with good anorectal outcomes, enabling the morbidity burden from CS to be reduced.

To the best of our knowledge, this study is the largest cohort study assessing bowel symptoms, sphincter integrity and anorectal function among women who underwent a subsequent delivery following index OASIs. We are only aware of only two other studies that have used bowel symptoms, anorectal function and sphincter integrity in both their antenatal assessment to recommend mode of delivery using a structured protocol, and then in the postnatal assessment for the evaluation of outcomes [11, 12]. These studies included 59 and 50 women respectively [11, 12]. Both of these studies showed no worsening of bowel symptoms or anorectal physiology when women were appropriately selected for VD following OASI using comprehensive assessment methods. Their results are consistent with our findings. A key difference in our protocol for this study and indeed the RCOG guidelines and all other published work is the advice given to symptomatic women with normal anorectal physiology [7, 12]. According to our protocol, symptomatic women with normal anorectal physiology, defined as an incremental pressure of >20 mmHg and no defect on EAUS, may be advised to have a VD.

Although in-depth antenatal and postnatal assessment is important, equally important is how this information is then used to counsel women regarding mode of delivery. Fitzpatrick et al. recently published a study that used validated symptom scores, EAUS and manometry in the antenatal period to help inform decision-making with regard to subsequent mode of delivery [18]. The criteria used enabled antenatal anorectal physiology results and symptom scores to suggest which women should have a VD versus CS in clear cut cases. The use of this particular set of criteria, however, left a relatively large number of “equivocal” cases in which decision-making was once again, and by admission of the authors, left to a variety of assessment methods that are neither validated nor consistent. The uncertainty regarding management for this group of women was evident in a paper reporting the recommendations for mode of subsequent delivery from a large UK survey [19]. Although clinical judgement and patient-centred care are always imperative, one of the strengths of our study is that it is the largest study to date to report the outcomes of using a protocol to aid clinicians in recommending mode of subsequent delivery that leaves no “equivocal” group of women. This is important, as it is this very group of women in which clinical practice is likely to vary widely in the absence of a robust evidence base.

It is to this end that we decided to perform a subgroup analysis looking at outcomes for symptomatic women with normal anal manometry and EAUS, who delivered by VD versus CS. This analysis is unique, with other published literature reflecting the guidelines of the RCOG (which by its own admission lack a strong evidence base) recommending that symptomatic women deliver by CS [7]. It is important to remember that although CS broadly speaking prevents further damage to the pelvic floor, it carries a burden of potential morbidity for which women should also be counselled. The CS rate for women included in our study was 19%. This rate is significantly lower than the 50% CS rate of Karmarkar et al., who used the same antenatal assessment methods, but a less detailed protocol [18].

We would also argue that a fourth-degree tear does not preclude vaginal delivery, as has been cautioned in the past [20]. In our cohort, there were 9 fourth-degree index tears. Six of these were recommended CS; 3 were recommended VD (2 asymptomatic with normal anorectal physiology tests and 1 with minor symptoms and normal anorectal physiology tests). We would advocate that referral to a unit able to provide full antenatal assessment with anal manometry and EAUS is essential before making a recommendation on mode of delivery for these women.

We are not aware of any publications that have given consideration to the relevance of IAS defects when recommending mode of delivery. Although the IAS plays a role in maintaining resting pressure, our results show that as long as the EAS is reasonably intact, an IAS defect does not have an impact on bowel symptoms or resting pressure in a subsequent pregnancy. The worsening of squeeze pressure in the VD group at 3 months postpartum for both the intact IAS and IAS defect group (Tables 6, 7, and 8), is consistent with the pattern seen for the whole cohort. We acknowledge that larger numbers are needed to draw firm conclusions, but until that is available it would appear that IAS defects do not predict an adverse outcome during subsequent vaginal delivery.

There is currently a huge variation in the advice given to pregnant women who have sustained a previous OASI and this is reflective of the weak evidence base [19]. A previous national survey showed a wide variation in clinical practice with regard to subsequent mode of delivery recommendations [20]. The RCOG guidelines have changed little from 2007 to 2015, reflecting the fact that the evidence base has not progressed much [7, 8]. A recent survey showed that >50% of respondents did not have a dedicated perineal clinic at their hospitals and did not routinely use symptom questionnaires, anal manometry or EAUS during the follow-up of OASIs [21]. It is a fair assumption that wide-ranging clinical practice still exists.

The strength of this study is in the in-depth information it provides on anorectal symptoms, sphincter function and integrity following subsequent delivery as a result of our rigorous antenatal and postnatal assessment. It therefore has great clinical utility, as we have shown that our framework for managing women in a subsequent pregnancy has resulted in good clinical outcomes for women. We acknowledge that EAUS and anal manometry has financial and workforce implications. However, it has been shown that EAUS has added value as it identifies women in whom OASI has been over-diagnosed and these women can be reassured that they actually sustained a second-degree tear [22]. As a compromise, it may be possible to offer a vaginal delivery to women who are asymptomatic and have good sphincter tone on examination. However, we have previously shown that digital examination has a poor positive predictive value and sphincter injury can be under-diagnosed [23]. Furthermore, at least 10% of women who are asymptomatic in the short term develop anal incontinence by 3 years and this is related to persistent sphincter defects [24]. We advocate that it is imperative for anyone with anorectal symptoms in the absence of an underlying pathological condition such as irritable bowel syndrome to be referred to a centre able to perform full anorectal assessment.

There are limitations to this study. Short-term follow-up is reported and therefore does not provide information on longer-term anorectal symptoms and function. We plan to perform a longer-term follow-up of these women to establish the natural history of subsequent delivery on anorectal symptoms. However, a prospective study by Reid et al., showed no deterioration of anorectal symptoms between 14 weeks postpartum and at 3 years postpartum [24].

Of the 351 women seen in the antenatal period following index OASI, only 169 attended for postnatal follow-up. This is largely due to a number of patients being referred from other centres to our tertiary referral unit. This cohort is still considerably larger than previous studies assessing sphincter integrity, anorectal symptoms and function following a subsequent pregnancy.

Finally, as with all other subsequent pregnancy studies to date, this study is limited by its design. Although a randomised controlled trial would be ideal, in the absence of this option we have aimed to minimise bias as much as possible. This has reduced the potential number we have included in our final analysis, but we aimed to reduce confounding and provide the best evidence that we could within the constraints of a prospective cohort study.

In summary, this study showed that there was no significant worsening of bowel symptoms, anorectal function and sphincter integrity at 12 weeks postpartum, apart from lower squeeze pressures at 3 months postpartum in the VD group among women who complied with the recommended mode of delivery as per our standardised protocol. In the absence of a randomised study, this information and the above protocol will aid clinicians and women in their decision-making regarding subsequent mode of delivery.