Identification of women at high risk for severe perineal lacerations.

Objectives: To evaluate the frequency and to identify the risk factors of severe perineal lacerations and the subgroup of women exposed to the highest risk for these complications.
Study Design: We conducted a case-control study in a large cohort of women for which vaginal delivery management consisted in systematic perineal support and restrictive use of mediolateral episiotomy. The case group comprised women with severe perineal lacerations while the control group comprised women without severe perineal lacerations. Maternal, labor, delivery and neonatal characteristics were analyzed in logistic regression models and a classification and regression tree (CART) was constructed.
Results: Between 2000 and 2009, 19,442 women delivered vaginally in our centre, 88 of whom had severe perineal lacerations (0.5%). Instrumental delivery (aOR 4.17, 95% CI 2.51-6.90), nulliparity (aOR 2.58, 95% CI 1.55-4.29), persistent posterior orientation (aOR 2.24, 95% CI 1.02-4.94) and increased birth weight (aOR 1.28, 95% CI 1.03-1.60) were independent risk factors of severe perineal lacerations whereas mediolateral episiotomy had a protective effect (aOR 0.38, 95% CI 0.23-0.63). CART identified instrumental delivery of neonates smaller than 4500 g in persistent posterior orientation in nullipara without mediolateral episiotomy as the clinical situation associated with the highest risk of severe perineal lacerations (12.5%). Conversely, patients with the lowest risk (0.1%) were those delivering spontaneously, neonates larger than 3200 g after mediolateral episiotomy.
Conclusions: Instrumental delivery, nulliparity, persistent posterior orientation and increased birth weight are independently associated with severe perineal lacerations. Restrictive use of mediolateral episiotomy protects against severe perineal lacerations especially in case of instrumental delivery.
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