Associations Between Maternal Obesity and Race, with Obstetric Anal Sphincter Injury: A Retrospective Cohort Study

This retrospective cohort study examined associations between maternal body mass index (BMI), race, and obstetric anal sphincter injury (OASI) (3rd/4th degree perineal lacerations). Obstetric anal sphincter injury may lead to significant maternal morbidity, and a more thorough understanding of risk factors for this complication may guide providers in patient counseling and procedures such as episiotomy or operative vaginal delivery. Vaginal deliveries performed at Kapi'olani Medical Center for Women and Children from 2008-2015 were included. Maternal body mass index at delivery was used and OASIs identified through International Classification of Diseases codes. Demographic/clinical variables were summarized through descriptive statistics. Adjusted odds ratios were calculated using multiple logistic regression. Of the 25,594 deliveries included, 1,198 (4.7%) involved an OASI. OASI prevalence differed by BMI (P < .0001). The prevalence was highest in women with BMI < 30 kg/m² (5.3%) and then decreased as BMI increased with women with BMI ≥ 50 demonstrating the lowest prevalence (1.7%). Compared to women with BMI < 30 kg/m², women with BMI > 50 kg/m² had a lower odds of OASI (OR 0.31 [95%CI 0.11 - 0.83]), which persisted after adjustment (aOR 0.28 [95%CI 0.08-0.96]). OASI also differed by race (P < .0001), with Native Hawaiian and other Pacific Islanders (NHOPI) demonstrating the lowest prevalence (3.0%) and Asians the highest (5.6%). After adjustment, compared to White women, NHOPI women had lower OASI prevalence that met the borderline of statistical significance (aOR 0.79 [95%CI 0.62-1.01]), while Asian women continued to demonstrate increased prevalence (aOR 1.50 [95% CI 1.22-1.85]). We conclude that obese women, including those with BMI ≥ 50 kg/m², have lower OASI prevalence. Race is also a significant factor, with Asians almost double the prevalence of NHOPIs. These findings contribute to evidence-based, individualized patient counseling on OASI.