Risk factors associated with severe perineal lacerations during vaginal delivery: A 10 years propensity score-matched observational study

Abstract BACKGROUND: Severe perineal lacerations are rare obstetric complications in high-income countries, yet, their prevention is crucial due to their long-term consequences on woman digestive function, sexual-mental health and wellbeing. This study aims study to assess the incidence of obstetric anal sphincter injuries at a single institution over a period of ten years and identifying women more at risk by evaluating the relationship between antenatal and intrapartum risk factors and severe perineal tears. METHODS: This was an observational retrospective cohort study carried out at a University Teaching Hospital in Italy in the period 2009-2019 using a prospectively maintained database. The study cohort included all women with singleton pregnancy at term who delivered by vaginal delivery in cephalic presentation. Two stages comprised the data analysis: a propensity score matching and a stepwise univariate and multivariate logistic regression. A secondary analysis was performed to further evaluate the effect of parity, epidural anaesthesia and duration of second stage.RESULTS: Of 41,440 patients screened for eligibility, 22,156 women met the inclusion criteria. Among them, obstetric anal sphincter injuries occurred in 81 (0.4%) cases: 51 (0.3%) after spontaneous delivery and 30 (0.5%) after vacuum delivery. There was an increased odd of severe lacerations for nulliparous women delivering by vacuum delivery (aOR 2.85, 95% CI 1.19,6.81; p=0.019), with reciprocal reduction in multiparous women with spontaneous vaginal delivery (aOR 0.35, 95% CI 0.15,0.84; p=0.019), Epidural anaesthesia and episiotomy were associated with a lower incidence of obstetric anal sphincter injuries (aOR 0.54, 95% CI 0.33, 0.86; p=0.011; (aOR 0.20, 95% 0.11, 0.36; p <0.001). The risk of severe lacerations was independent from the duration of the 2nd stage (aOR 1.0, 95% 0.99, 1.0; p=0.3). Neonatal risk factors include head circumference (OR 1.5, 95% CI 1.18,1.90; p=0.001) and vertex malpresentation (aOR 2.71, 95% CI 1.08,6.78; p=0.033). Induction of labour (aOR 1.13, 95%CI 0.72, 1.92 p=0.6), frequent obstetric examinations (aOR 1.17, 95% CI 0.72, 1.9 p=0.5), and women’s supine station at birth were additional contributors (aOR 1.25, 95% CI 0.61, 2.55 p=0.5). Amongst severe obstetric complications, shoulder dystocia increased the risk of obstetric anal sphincter injuries by nearly four times (aOR 3.92, 95% CI 0.5 ,30.74; p= 0.2) whilst postpartum hemorrhage occurred three times more often in cases of delivery complicated by severe lacerations (aOR 3.35, 95% CI 1.76,6.40; p<0.001). The association between obstetric anal sphincter injuries, parity and the use of epidural anaesthesia was confirmed in a secondary analysis. We found that primipara who delivered without epidural anaesthesia had the highest risk of obstetric anal sphincter injuries (aOR 2.53, 95%CI 1.46, 4.39; p=0.001)CONCLUSIONS: Severe perineal lacerations were rare complication of vaginal delivery. Using a robust statistical model, we investigated a broad range of antenatal and intrapartum risk factors, including factors that are usually underreported. We found that women who delivered for the first time without epidural anaesthesia had the highest risk of obstetric anal sphincter injuries