Perineal body length and lacerations at delivery

OBJECTIVE: To define normal perineal body length during labor and determine if a shortened perineal body is associated with perineal lacerations or operative vaginal delivery. STUDY DESIGN: We reviewed charts of patients admitted for labor over a 4-month period. The perineal body was measured by the admitting physician and delivery outcomes obtained from inpatient records. Patients were excluded for malpresentation, multiple gestation, gestational age <36 weeks, incomplete records and scheduled cesarean delivery. To determine if differences existed between patients with perineal body measurements available and those without, X 2 analysis was used, with P<.05 considered significant. Multiple logistic regression was used to control for confounding variables and determine if a shortened perineal body affected the incidence of operative vaginal delivery and significant lacerations at vaginal delivery. RESULTS: A total of 234 patients met our inclusion criteria; perineal body measurements were available for 133 (57%). The average perineal body length was 3.90 cm (±0.70). Patients with a perineal body of ≤ 2.5 cm had a significantly higher chance of sustaining a third- or fourth-degree laceration (40% vs. 5.6%, P=.004). This risk remained after controlling for both operative vaginal delivery and episiotomy. The incidence of operative vaginal delivery was greater (28.5% vs. 9.2%, P=.006) for patients with a perineal body ≤ 3.5 cm. CONCLUSION: There is an increased risk of significant lacerations and operative vaginal delivery in patients with a shortened perineal body.