RESUMEN
OBJECTIVE: To assess the risk for obstetric anal sphincter lacerations in relation to maternal obesity among primiparous women in Sweden. DESIGN: A population-based study. SETTING: Sweden. POPULATION: All women with vaginal delivery and singleton pregnancy in Sweden in the years 2003-2008 (n = 210,678). METHODS: The Medical Birth Registry, the National Board of Health and Welfare, was used to identify cases of rupture and body mass index (BMI) classes. The population was categorised into four classes with BMI of <25, 25 to <30, 30 to <35 and >35 kg/m². MAIN OUTCOME MEASURES: Odds ratios were estimated with 95% confidence intervals. In order to estimate the effect of BMI on obstetric anal sphincter lacerations, with possible confounders accounted for, uni- and multivariate logistic regressions were performed. RESULTS: In total, 8958 (4.25%) cases of anal sphincter lacerations (grade III-IV) occurred; increasing BMI showed a significant near-dose-response type of protective effect against grade III-IV lacerations when compared with women with BMI <25 kg/m²: BMI 25 to <30 kg/m², 0.89; BMI 30 to <35 kg/m², 0.84; BMI > 35 kg/m², 0.70. CONCLUSION: Overweight and obesity were associated with a decreased risk for obstetric anal sphincter lacerations.