Hypothesis / aims of study
National guidelines advocate for individualised multidisciplinary assessment following obstetric anal sphincter injuries (OASIS), yet evidence evaluating whether structured specialist pathways translate these recommendations into practice remains limited. OASIS represents the most severe form of perineal trauma associated with vaginal delivery, with long-term consequences including anal incontinence, pelvic floor dysfunction, and impaired quality of life. Determining the safest mode of delivery in subsequent pregnancies remains one of the most clinically challenging decisions following OASIS, requiring assessment of symptom severity, endoanal ultrasound findings, and anorectal function. Real-world evidence on adherence to clinical delivery recommendations and factors influencing reproductive decisions remains insufficient. This study aimed to evaluate adherence to mode of delivery recommendations within a structured tertiary OASIS pathway over a 15-year period, and identify factors associated with future pregnancy decisions.
Study design, materials and methods
This was a retrospective cohort study at a single tertiary centre between 2009 and 2024. A total of 1,506 women with a documented OASIS were included. All women entered a structured postnatal care pathway: specialist pelvic floor clinic review at 12 weeks postpartum, validated symptom questionnaires (St Mark's Incontinence Score and Obstructed Defaecation Syndrome Score), endoanal ultrasound and anorectal manometry. Each case was discussed at a multidisciplinary team meeting before personalised delivery recommendations were formulated. Women were followed up at approximately 9 months postpartum. Data on subsequent pregnancies and mode of delivery were extracted from electronic health records. Chi-square tests were used for categorical variables and Mann-Whitney U tests for ordinal and non-normally distributed variables; significance was set at p<0.05.
Results
Of 1,502 women with complete follow-up data, 415 (27.6%) had a subsequent pregnancy. Among these, 69.9% adhered to the recommended mode of delivery, with 58.2% undergoing an assisted delivery (planned caesarean section or assisted vaginal birth). The recommendation to avoid vaginal delivery was given to 71.0% in both groups (p=0.99). Ethnicity differed significantly between groups (p=0.03): White British/Irish and Black women were more represented in the pregnancy group (35.1% and 19.2% respectively), while White Other women were more prevalent in the non-pregnancy group (25.6%). External sphincter defect extent differed significantly (p=0.007); women with a subsequent pregnancy were less likely to have the entire length of the external anal sphincter affected (44.6% vs 56.4%), and more likely to have majority extent. No significant differences were found in bowel or urinary symptoms, level of tear, sphincter repair, or St Mark's Incontinence Score.
Interpretation of results
A 69.9% adherence rate supports the effectiveness of a structured multidisciplinary post-OASIS pathway in guiding delivery decision-making. This is consistent with literature demonstrating that women with higher-grade perineal trauma more commonly choose caesarean section in subsequent pregnancies [1], and with evidence that adherence to recommended delivery modes is not associated with deterioration in anorectal function [2]. Associations between ethnicity and reproductive decisions, and between sphincter defect severity and future pregnancy rates, highlight potential disparities in healthcare access and culturally influenced decision-making. Nearly a third of women did not adhere to clinical advice, reflecting the influence of personal preferences, previous birth experiences, and psychosocial factors. The absence of differences in symptom profiles suggests symptom burden alone does not determine reproductive choices, reinforcing the need for counselling beyond clinical findings.
Concluding message
This large-scale study demonstrates that a structured specialist OASIS pathway achieves high adherence to mode of delivery recommendations, supporting its value as a model of post-OASIS care. Ethnicity and sphincter defect severity were associated with future pregnancy decisions, underscoring the importance of culturally sensitive, individualised counselling. These findings complement existing evidence on delivery outcomes after OASIS [3] and contribute to the case for investment in specialist OASIS services. Future research should explore psychosocial determinants of non-adherence to ensure pathways remain equitable, holistic, and patient-centred.