Development of a Risk Score to Predict Obstetric Anal Sphincter Injuries in Laboring Patients [8OP]

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We piloted the utility of a scoring system to predict patient risk of obstetric anal sphincter injury (OASIs) during labor.


Among the 9,800 women with singleton term cephalic vaginal deliveries within Kaiser Permanente Northern California between January and December 2013 with complete study data, 8.5% (n=833) of the nullipara and 3.5% (n=343) of the multipara incurred OASIs. Multivariable logistic regression and classification and regression tree analyses were used to identify risk factors. Maternal and gestational age, race/ethnicity, duration of second stage of labor, vacuum delivery, and history of OASIs were associated with OASIs. Stratified by parity, points were assigned to each risk factor as an integer on a 10-point scale based on effect size and impact in the regression analyses, and were externally validated within a similar separate patient cohort using multivariable logistic regression.


Different OASIs risk score cut-offs were assessed. Among nulliparous women, a score ≥6 had 40% sensitivity and 91% specificity, whereas a score ≥4 had 51% sensitivity and 84% specificity. Among multiparous women, a score ≥7 had 89% sensitivity and 60% specificity compared to a score ≥10, which had 74% sensitivity and 72% specificity.


These pilot scores, demonstrating a reasonable predictor of OASIs risk, illustrate the utility of a clinical risk score to inform providers of patients' risk of OASIs prior to delivery and facilitate a shared decision-making approach to labor management.

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