Objective: To assess the incidence and risk factors for third- and fourth-degree perineal tears (34DPT), and to identify subgroups of women who are at especially high risk for 34DPT.
Methods: A cohort study of women who underwent vaginal delivery in a single tertiary medical center between 1999 and 2011, (58 937 deliveries). Women diagnosed with 34DPT following delivery were compared to control group. Multivariate logistic regression analysis and tree classification analysis were used to identify combinations of risk factors which were associated with considerable risk for 34DPT.
Results: Overall, 356 (0.6%) deliveries were complicated by 34DPT (340 (95.5%) third-degree tears and 16 (4.5%) fourth-degree tears). Independent predictors of 34DPT were: forceps delivery (odds ratio (OR) = 5.5, confidence interval (CI) 3.9-7.8), precipitate labor (OR = 5.2, CI 2.9-9.2), persistent occiput posterior position (OR = 2.6, CI 1.6-4.3), vacuum extraction (OR = 1.9, CI 1.4-2.6) as well as large for gestational age (LGA) infant and gestational age > 40 weeks. Fourth-degree tears were associated with forceps delivery (OR = 12.5, CI 2.3-66.2), precipitate labor (OR = 9.7, 95%-CI 1.2-75.4) and LGA infant (OR = 7.4, 95%-CI 1.7 -1.5). Overall, the predictability of 34DPT was limited (R(2 )= 0.4). In subgroups of women with certain combinations of risk factors the risk of 34DPT ranged from 10% to 25%.
Conclusion: Despite the limited predictability of 34DPT by individual risk factors, the use of combinations of risk factors may assist obstetricians in identifying women who are at especially high risk for 34DPT.