Clinical Grade of Obstetric Anal Sphincter Injuries and Prediction of Mode of Birth Recommendations: A 20-Year Retrospective Analysis

Abstract

Objective: To determine whether assessment of symptoms and clinical grade of obstetric anal sphincter injuries (OASIs) is predictive of subsequent endoanal ultrasound (EAUS) and anal manometry (AM) findings to guide mode of birth recommendations.

Design: Twenty-year retrospective analysis.

Setting: Tertiary urogynaecology unit.

Population or Sample: Women (n = 607) with a history of OASI in the second half of a subsequent pregnancy, 2002–2022.

Methods: A St Mark's Incontinence Score (SMIS), AM and EAUS were completed. An elective caesarean section (ELCS) was recommended if there was an external anal sphincter (EAS) defect and an incremental maximum squeeze pressure (IMSP) < 20 mmHg.

Main Outcome Measures: Accuracy, sensitivity, specificity, negative and positive predictive values (NPV and PPV) with 95% CI were calculated for the assessment of anorectal symptoms and clinical grade of tear relative to EAUS and AM findings.

Results: Accuracy of symptom assessment and clinical grade of tear in determining those with an EAS defect and IMSP < 20 was 75.4% (95% CI 69.3%), 69.6% (95% CI 63.8%–75.0%), 62.7% (95% CI 50.0–74.2) and 43.6% (95% CI 27.8%–60.4%) with 3a, 3b, 3c and fourth degree tears, respectively. 3a tears had the highest NPV for EAS defect and IMSP < 20 (100.0% [95% CI 97.9–100.0]), EAS defect alone (97.1% [95% CI 94.7%–98.4%]) and IMSP < 20 alone (93.5% [95% CI 90.1–82.1]).

Conclusions: Symptom assessment and clinical grade of OASI cannot be used solely to guide mode of delivery recommendations in a subsequent birth. Absence of symptoms in women with 3a tears has a high NPV, meaning these women can be recommended a vaginal birth.