678: The influence of ethnicity on rates of obstetric anal sphincter injury

Obstetric anal sphincter injuries (OASIS) are a leading cause of anal incontinence and a significant source of medico-legal claims, especially in cases where there is failure to recognize and/or adequately repair the defect. Identification of prenatal risk factors may reduce the incidence and increase recognition in higher risk groups. Risk factors such as high birthweight and instrumental delivery are well established; less is known regarding the risk in ethnic subgroups. The objective of this study was to examine the association between ethnicity and rates of OASIS. All nulliparous term (≥37 weeks) singleton liveborn deliveries over a 6 year period at a large tertiary referral centre were included. Baseline demographic and delivery details were recorded on an anonymized computerized database, these data are subject to continuous audit. Rates of OASIS were compared between various ethnic subgroups, including Caucasian, Asian, South Asian (including Indian and Pakistani), Chinese and African populations. Unpaired t-tests were used to compare continuous data and chi-square tests to compare categorical data. Multiple logistic regression was used to calculate adjusted odds ratios. In total there were 22,991 singleton nulliparous term deliveries during the study of whom 17,697(77%) had a vaginal delivery and were included in analysis. Ethnicity data was available for 12,361(70%). Data on OASIS were recorded for all women including those where ethnicity data were not available to exclude ascertainment bias. The overall incidence of OASIS was 2.9%. A breakdown of the incidence of OASIS is included in Table 1. In Caucasian women the incidence of OASIS was 3%(331/11153). Mode of delivery, birthweight and ethnicity were all associated with the development of OASIS; no association with BMI was observed. The highest incidence of OASIS was observed in the South Asian cohort with an incidence of 8.1% [(14/172), p<0.001, OR 2.9, 95%CI 1.65-5.1]; this remained significant following adjustment for significant cofounders. We conclude that being of South Asian ethnicity confers a significantly increased risk of sphincter damage when compared to a Caucasian population. The identification of at-risk groups allows for senior input at delivery to ensure adequate recognition and appropriate follow up. Our findings would suggest that a low index of suspicion in South Asian women is needed, particularly in cases with additional risk factors.