Risk factors associated with third- and fourth-degree perineal lacerations in singleton vaginal deliveries: a comprehensive United States population analysis 2016-2020

Objectives: Perineal lacerations are a common complication of vaginal birth, affecting approximately 85 % of patients. Third-and fourth-degree perineal lacerations (3/4PL) remain a significant cause of physical and emotional distress. We aimed to perform an extensive assessment of potential risk factors for 3/4PL based on a comprehensive and current US population database. Methods: Retrospective population-based cohort analysis based on the US Centers for Disease Control and Prevention Natality Live Birth online database between 2016-2020. Baseline characteristics were compared between women with 3/4PL and without 3/4PL by using Pearson's Chi-squared test with statistical significance set at p<0.05. Bonferroni correction was used to account for multiple comparisons. Multivariable logistic regression was performed to evaluate the association between a variety of potential risk factors and the risk of 3/4P. Results: Asians/Pacific Islanders had the highest risk of 3/4PL (2.6 %, aOR 1.74). Gestational hypertension and pre-eclampsia were associated with increased risk of 3/4PL (aOR 1.28 and 1.34, respectively), as were both pre-gestational and gestational diabetes (aOR 1.28 and 1.46, respectively). Chorioamnionitis was associated almost double the risk (aOR 1.86). Birth weight was a major risk factor (aOR 7.42 for greater than 4,000 g), as was nulliparity (aOR 9.89). Conclusions: We identified several maternal, fetal, and pregnancy conditions that are associatedwith an increased risk for 3/4PL. As expected, nulliparity and increased birth weight were associated with the highest risk. Moreover, pregestational and gestational diabetes, hypertensive disorders of pregnancy, Asian/Pacific Islander race, and chorioamnionitis were identified as novel risk factors.