Perineal body length and perineal lacerations during delivery in primigravid patients.

This study assessed the relation between perineal body length and the risk of perineal laceration extending into the anal sphincter during vaginal delivery in primigravid patients at an institution with a low utilization of episiotomy. This was a prospective study of primigravid patients in active labor. Primigravid women with singleton pregnancies who were in the first stage of labor at 37 weeks gestation or greater were recruited, and the admitting physician measured the length of the perineal body. The degree of perineal laceration and other delivery characteristics were recorded. Data were analyzed using univariate analyses, receiver-operator curve analyses, and multiple logistic regression for factors associated with increased severity of vaginal lacerations. The perineal body length, duration of second stage of labor, type of delivery, and patient age were associated (P < 0.1) with third- and fourth-degree (severe) perineal lacerations in primigravid women using receiver-operator curve analysis. Using logistic regression, only the duration of second stage of labor and length of the perineal body were significant (P < 0.04) predictors of third- and fourth-degree lacerations, with odds ratios of 32 (1.3 to 807 as 95% CI) and 24 (1.3 to 456), respectively. Both a perineal body length of ≤3.5 cm and a duration of second stage of labor >99 minutes were associated with an increased risk of third- and fourth-degree lacerations in primigravid patients.