DISCUSSION
IBS is chronic functional gastrointestinal tract disorder which causes abdominal pain and alteration to bowel habit in 10-15% of the population, which is in keeping with the results of our study. There is also a greater preponderance toward women, with some estimates suggesting more than half are without a formal diagnosis. [9] Our findings demonstrate that patients with IBS have significantly worse faecal incontinence after primary OASIS repair. Women without IBS did not show significant difference in faecal incontinence after primary OASIS repair compared to controls. Uniquely we have also shown that the presence of IBS in post caesarean section in primigravid patients – in whom there were no sphincter injuries – also demonstrated higher faecal incontinence scores albeit more modestly. Lastly we have shown that persistent sphincter defects after primary OASIS repair did not correlate to worse faecal incontinence scores. [10]
OASIS causes both short and long-term complications after childbirth such as perineal pain, dyspareunia, faecal and urinary incontinence; in addition to emotional and psychological effects. [11, 12] Immediate surgical repair by experienced obstetricians or colorectal surgeons trained in sphincter tissue recognition within 12 hours is considered the gold standard, either using an overlapping or end-to-end technique. [13, 14] The exact incidence of faecal incontinence after OASIS is likely under-reported as some patients feel unable to discuss their symptoms with a medical professional. [15]
OASIS are classified within the spectrum of perineal tears. The internationally accepted classification of obstetric perineal trauma is as follows [4]: first degree – laceration of vaginal epithelium or perineal skin, second degree – involvement of perineal muscles, third degree – disruption of <50% external sphincter (IIIa), >50% external sphincter (IIIb), or both external and internal sphincter (IIIc), and most severe fourth degree – disruption of anal epithelium. Previous studies have suggested that grading of obstetric sphincter injuries can help prognosticate quality of life and manometry outcomes. [16, 17] The risk of sphincter defects following vaginal delivery may be as high as 26% and up to half of these are missed on routine physical examination immediately post-partum, however women with IBS are at no increased risk of obstetric sphincter injury. [10, 18]
When assessing women with different grades of sphincter defect on ultrasound, our findings reveal no significant difference in mean Wexner scores compared to women without sphincter defects. Roos et al [17] report comparable rates of incontinence and sphincter defects to our population, however they found that a combined IAS and EAS defect resulted in worse faecal incontinence after a mean follow up of 9 weeks. Our study used more liberal criteria to define ultrasonographic residual sphincter defects in the absence of standardised and clinically validated residual defect definitions. Our study confirms claims of other studies that ultrasonographic sphincter defects may not reliably correlate with increased severity of faecal incontinence after the initial post-partum period [19, 20]. Our findings provide evidence that after OASIS repair, screening for presence of IBS may be more valuable than ultrasonography in predicting those at risk of worse long-term faecal incontinence which could facilitate more targeted behavioural, dietary, or pharmacological intervention.
We found that women who are unable to delay defaecation experience more severe faecal incontinence. Faecal urgency occurs due to unexpected contractions within the rectum and subsequent relaxation of the anal canal. A population-based study by Bharucha et al [19] support our findings, identifying urgency as a significant risk factor for post-partum faecal incontinence. In a healthy rectum, intraluminal pressure beyond 300 millilitres results in a feeling of urgency. [21] Although not extensively studied, the effects of hormonal changes intra- and post-partum are also believed to influence gastrointestinal tract function in women with IBS. For example, oestrogen influences the gut-brain axis which upregulates visceral hypersensitivity and mucosal immune activation. [22] Manometry reveals increased mucosal sensitivity to electrical stimulation of the upper anal canal compared to parous women without IBS. [10] These factors may therefore lower the threshold required for urgency to occur and synergistically increase the risk of faecal incontinence following OASIS repair.
A major strength of this study was the dual versatility of the questionnaire which allowed standardisation of subjective symptoms by calculation of a Wexner score, and also diagnosing IBS based on Rome IV criteria. This ensured that patients who may not have a formal diagnosis of IBS (which as stated earlier is not infrequent) were appropriately categorised to increase accuracy of our results. An additional strength of the study was the mean follow up interval of over two years, which facilitated assessment of symptoms beyond the commonly studied early post-partum period.
A limitation to the present study was the predominance of younger patients in the control groups, as it is known that the risk of faecal incontinence increases with age [3]. Mean Wexner scores were significantly higher in the older Group A, but linear regression analysis allowed control for this variable and age did not significantly alter faecal incontinence scores in our cohort. Another limitation is the single centre design which may be improved by future research utilising a multi-centre design and recruiting a larger sample size.