The aim of this study was to compare the long-term prevalence of fecal incontinence and other pelvic floor disorders in women with one or two consecutive obstetric anal sphincter injuries (OASI) in comparison with women without sphincter injury.

This nationwide register and questionnaire survey in Swedish women was conducted in 2015. The Swedish National Board of Health and Welfare was requested to identify the potential study population from the Swedish Medical Birth Register (MBR). Non-pregnant 2-para women with singleton vaginal births between 1992 to 1998 with no previous or further births were identified (n = 64,687). A sample of 11,000 women was randomly selected by Statistics Sweden and invited to participate in the study by returning a postal questionnaire. The questionnaire was returned by 7,441 women.  There were 6,760 women with no OASI and 357 with one OASI (253 at the first and 104 at the second delivery) and 39 had 2 OASIs. To achieve equal numbers of women with one and two OASIs the latter group was oversampled by extending the calendar period for this cohort from 1987-2000. The total number of women with 2 OASIs was then 324. Given this size of the study cohorts, an alfa level of 0.05, a power value of 80%, and using Fisher’s exact test for the analysis, the minimum significant difference in prevalence of fecal incontinence was 5% when comparing the control group with either of the two OASI cohorts and 11% when comparing the two OASI cohorts only.   

OASI was retrieved from the MBR as code 664.2 and 664.3 (ICD-9), code O70.2 and O70.3 (ICD10), and from the Nordic Medico-Statistical Committee’s (NOMESCO’s) surgical code MBC33 “Repair of complete rupture of perineum, Grade 3 and 4 injuries”. The postal and web-based 40-item questionnaire included questions about current symptoms of fecal and urinary incontinence and pelvic organ prolapse. Women were also asked about current height and weight, menstrual status, hysterectomy, menopause, and hormone treatment. Information from the questionnaire survey was combined with obstetric information in the MBR. Descriptive data for continuous variables were presented as mean and standard deviations. Categorical data was presented as numbers and percentages. Fisher’s exact test was used for comparisons of dichotomous variables and Students t-test for continuous variables when comparing two cohorts. Logistic regression analysis was used to analyse the risk of different pelvic floor disorders between the three groups. Results were presented as adjusted odds ratio and 95% confidence interval and adjusted p-values. Adjustment was made for age and BMI. Statistical significance was set at p < 0.05. When comparing all three cohorts, Mantel-Haenszel Chi-square test were used.

The overall response rate was 65%. Women with two OASIs were somewhat older, 50.6 (SD 4.2) years compared with those with one OASI 49.8 (SD 4.1) years, and those without OASI 49.1 (SD 4.0) years). There was no difference in BMI between groups. The mean follow-up time was 19 years and the shortest time since last birth was 14 years. Women with one and two OASIs were more often postmenopausal (29.4% and 30.2% respectively) compared with those without OASI, 22.7% (p=0.0044). The prevalence of fecal incontinence was 11.7% in women without OASI and 23.8% after one OASI (OR 2.29, 95% CI 1.77-2.97) and 36.1% after two OASIs (OR 1.76, 95%CI 1.25-2.48).  The rate of one and more pelvic floor disorders was higher after one or two sphincter injuries (50.7% and 55.6% respectively) compared with women without injury (42.5%, p=0.0039 and p<0.0001 respectively). Urinary incontinence with a duration of >10 years was more prevalent in women with one or two sphincter injuries (11.5% and 12.7% respectively), compared with women without OASI (8.3%, p=0.046 and p=0.0066 respectively). The prevalence of symptomatic pelvic organ prolapse was almost identical in all three groups (Table 1).

This study on long-term pelvic floor disorders in women with one or two consecutive sphincter injuries sustained at birth two decades earlier, showed that there was a dose-response relationship between OASI (no OASI, 1 OASI, 2 OASI) and fecal incontinence, and other pelvic floor disorders, including an earlier onset of urinary incontinence. However, the prevalence of symptomatic pelvic organ prolapse was unaltered.

There was a strong dose-response association between obstetric anal sphincter injury and fecal incontinence, with unacceptably high rates of fecal incontinence in the long-term. More than every third woman had fecal incontinence after a repeat OASI. In antenatal counseling women should be informed about the risk of fecal incontinence associated with OASI.