Objective: To analyze circumstances relating to severe anal sphincter tears occurring at spontaneous delivery, in view of reported differences in practice regarding manual perineal protection during delivery.
Design: Cohort study of midwife-conducted non-operative vaginal deliveries.
Setting: Five Norwegian hospitals with 12,438 consecutive deliveries during a 12-month period.
Methods: Data from 357 women sustaining third and fourth grade anal sphincter tears (2.9%) were analyzed.
Main outcome measures: Different incidence of major perineal tears.
Results: Sphincter tear incidence varied significantly between the five hospitals, from 1.3 to 4.7% (p<0.001, RR=3.14 (CI: 2.38-5.56)). There was no significant difference between the five hospitals when other risk variables were compared. Use of oxytocin in the second phase of labor and of epidural analgesia was significantly more often applied in the hospital with the lowest rate of sphincter tears. The midwives' perception of having applied perineal support was not significantly different between the two hospitals with the highest and the lowest incidence of sphincter tear.
Conclusion: The observed difference in incidence of sphincter tear between the hospitals remains unexplained, but could be due to different perineal protection handling techniques.