Hypothesis / aims of study
Anal incontinence after vaginal delivery is a major concern for many women. Anal incontinence is defined as the involuntary or uncontrolled loss of mucus, liquid or solid stool or the passage of gas (1). It is supposedly an underreported condition because of its stigmatizing role (2). It occurs in approximately 50% of women at long-term follow-up after anal sphincter ruptures. The prevalence of anal incontinence six months postpartum has been reported to be as high as 49% among primiparous women in general. Only about half the cases of anal incontinence after childbirth can be related to anal sphincter injuries and the remaining cases of anal incontinence must thus be related to other factors (3). However, the pathophysiological mechanisms of anal incontinence are still not fully understood and the condition remains an unsolved problem for many patients. The objective of this study was to examine the association between degree of perineal rupture and anal incontinence 12 months postpartum among primiparous women.
Study design, materials and methods
This study was a multi-center prospective cohort study conducted at four hospital units; two univer-sity hospitals and two general hospitals from July 2015 until January 2019.
A total of 574 primiparous women (193 with none/labia/1st degree ruptures, 192 with episiotomies/2nd degree ruptures, 189 with 3rd/4th degree ruptures) were included. Baseline data was ob-tained 2 weeks postpartum. Subjective symptoms of anal incontinence were evaluated 12 months postpartum by a web-based questionnaire (n=574) and a clinical examination of anal function using endoanal ultrasound scanning (n=499) and High Resolution anal manometry (n=482). Main outcome measurements were: Anal incontinence (St. Mark’s score >4), endoanal ultrasound find-ings (defect in internal and/or external anal sphincter muscles) and anal manometry findings (rest pressure, maximum squeeze pressure, maximum duration of squeeze).
Women suffering from an anal sphincter rupture had higher risk of anal incontinence compared to women with ruptures of lower degree, adjusted Relative Risk (aRR) 2.85, 95% CI 1.36-5.98. The risk of anal incontinence increased with 8% per one unit increase in body mass index, aRR 1.08, 95% CI 1.03-1.14. A rupture of degree 3c and 4 increased the risk of anal incontinence with aRR of 6.81 (95% CI 2.03-22.9) and aRR of 5.50 (95% CI 1.42-21.3), respectively. Patients with incontinence had a lower anal resting tone of 62.5 mmHg compared to 78.6 mmHg in women with no incontinence (p < 0.001).The values for maximum squeeze pressure in the two groups were 128.3 and 158.4 mmHg, respectively (p < 0.001).
Interpretation of results
Obese women are in higher risk of developing anal incontinence postpartum regardless degree of rupture compared to women of normal weight. Obesity is the most common health care problem in women of reproductive age. Maternal obesity has become highly prevalent worldwide and is a ma-jor concern in obstetrics. As a consequence, the number of adverse maternal outcomes must be expected to rise. Low anal pressure seems to indicate a defect in the external anal sphincter muscle or in the internal anal sphincter muscle , and as an ultrasound verified defect is associated with poorer outcome, it is important to identify the full extent of injury in women who sustain 3rd or 4th degree ruptures. Further, a particular attention to repair of defects in the internal anal sphincter muscle is needed. In this study, women who had sustained a grade 3c or 4 rupture had a poorer outcome compared to those who had sustained a grade 3a or 3b rupture or women with even smaller ruptures. It is therefore important to identify the full extent of injury at delivery, paying particular attention to repair of the internal anal sphincter muscle as a defect in the internal anal sphincter muscle is associated with increased risk of anal incontinence. We suggest that repairs should be performed in a theater under appropriate circumstances to optimize diagnosing and repair of the rupture. Moreover, routine follow‐up after repair of 3rd and 4th degree ruptures is important in order to tackle any defecatory problems at an early stage.
The present study also found that neither instrumental delivery nor episiotomy had any influence on the risk of developing anal incontinence 12 months postpartum, and the results support the ongoing initiative among midwives and obstetricians to minimize perineal ruptures during childbirth and avoid anal sphincter ruptures when possible.