Objective: Chinese women have been shown to have a higher incidence of severe perineal laceration compared to other ethnic groups. We sought to test the hypothesis that this risk is related to body mass index (BMI) or to a relative fetal-maternal size disproportion as measured by the ratio of the newborn birthweight to maternal BMI (BW:BMI).
Methods: A retrospective cohort study was performed using a pre-existing obstetric database. Third- and fourth-degree perineal lacerations served as the primary outcome of interest. Logistic regression was used to compare Chinese women to other ethnic groups and adjust for confounders.
Results: Three thousand and eighty-five singleton vaginal deliveries were identified, with BMI data available for 2281. Chinese women had a greater risk for severe perineal laceration compared to Caucasian (OR: 3.22; 95% CI: 0.73-14.32) and Hispanic women (OR: 2.88; 95% CI: 1.92-4.30). Multivariate analysis found that newborn birth weight plays a role (OR: 1.0012; 95% CI: 1.0007-1.0016), but BMI alone did not explain the discrepancy (P=0.89). However, the BW:BMI ratio appears to be a stronger predictor of laceration rate than either variable alone (OR: 1.011; 95% CI: 1.003-1.020).
Conclusion: The higher risk of severe perineal laceration in Chinese women compared to other ethnicities can be attributed, in part, to a relative fetal-maternal size disproportion.