Third and fourth degree perineal tears. Predictor factors in a referral hospital.

BACKGROUND: Tears of the anal sphincter are a feared complication of vaginal delivery, as many as 50% of these patients experience incontinence as an after-effect. Identifying significant predictor factors leading to third or fourth degree perineal tears during vaginal delivery was the objective of this study.

METHODS: During a two-year period (1995-1996), a third or fourth degree perineal rupture occurred in 214 women (3.7%) after vaginal delivery. Data from these deliveries were collected and compared to data from deliveries without anal sphincter tears in order to identify risk factors. A stepwise logistic regression model was used for the analysis.

RESULTS: Independent risk factors of significance were vaginal nulliparity, a squatting position on a delivery chair, maternal age exceeding 35 years, baby's birth weight over 4000 g, vacuum extraction (both outlet and mid release), median episiotomy, oxytocin augmentation and birthing between 3 a.m. and 6 a.m.

CONCLUSIONS: This study identified several factors associated with anal sphincter tears. Median episiotomy should be avoided. Delivery, while squatting on a low chair, should be used with caution. A woman with one or more risk factors requires caution by birth attendants during delivery. Gynecologists should consider the option of cesarean section instead of vacuum extraction, especially when mid release is needed in the presence of macrosomia. A continuous audit regarding instrumental delivery technique is necessary.