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OBJECTIVE: The objective of the study was to evaluate the frequency of

obstetrical anal sphincter injuries (OASIS) in women undergoing operative

vaginal deliveries (OVD) and to assess whether a mediolateral episiotomy

is protective for developing OASIS in these deliveries.

STUDY DESIGN: Weperformed a retrospective cohort study. Maternal and

obstetrical characteristics of the 2861 women who delivered liveborn infants

by an OVD at term in the years 2001-2009 were extracted from a clinical

obstetrics database and were analyzed in a logistic regression model.

RESULTS: The frequency of OASIS was 5.7%. Women with a mediolateral

episiotomy were at significantly lower risk for OASIS compared with

the women without a mediolateral episiotomy in case of an OVD (adjusted

odds ratio, 0.17; 95% confidence interval, 0.12- 0.24).

CONCLUSION: We found a 6-fold decreased odds for developing OASIS

when a mediolateral episiotomy was performed in OVD. Therefore, we

advocate the use of a mediolateral episiotomy in all operative vaginal

deliveries to reduce the incidence of OASIS.