Determinants of the length of episiotomy or spontaneous posterior perineal lacerations during vaginal birth

The objective of this study was to measure the length of episiotomy or spontaneous posterior perineal laceration and their relationship to perineal measurements and obstetric variables. The length of the perineum and genital hiatus and vertical length of episiotomy or posterior perineal tears were measured in 114 consecutive parturients with spontaneous singleton term deliveries. Seventy-four (65%) women underwent episiotomy while 40 (35%) sustained spontaneous posterior tears. Perineal or genital hiatus length was significantly correlated to episiotomy (r=0.34, p=0.003) or laceration (r=0.37, p=0.02) length, respectively. This association was significant (p=0.001) in a generalized linear model with duration of second stage of labor (p=0.005), degree of tear (p=0), and parity (p=0). Perineal length was significantly related to maternal age (p=0.036) and weight (p=0.037) and hiatal length (p=0). Short perineum and genital hiatus, long second stage of labor, and low parity are associated with longer posterior perineal injury.