INTRODUCTION: Approximately 85% of vaginal deliveries are accompanied by perineal trauma. The objective of this trial was to compare the incidence of perineal trauma after primary delivery of either the anterior or posterior shoulder during vaginal delivery.

MATERIAL AND METHODS: This was a randomized single-blinded trial comparing primary delivery of either the anterior or posterior shoulder in women having their first vaginal delivery. Primary outcome was any perineal trauma. Results were analyzed according to the intention-to-treat principle and supplemented with a per-protocol and as-treated analysis.

RESULTS: Between June 2013 and March 2015, 650 women were randomized, and 543 (posterior, n = 281; anterior, n = 262) were included in the final intention-to-treat analysis. Most group characteristics were similar. The frequency of any perineal trauma did not differ between the two groups (posterior: 91.5%, anterior: 90.5%; odds ratio 1.130, 95% confidence interval 0.628-2.032, p = 0.684). The results did not change after adjustment for basic characteristics with significant group differences (a1 odds ratio 1.174, 95% confidence interval 0.632-2.179, p = 0.612) or predefined risk factors (a2 odds ratio 1.139, 95% confidence interval 0.599-2.166, p = 0.691). The rate of perineal trauma also did not differ between the groups in a "per-protocol" and "as-treated" analysis.

CONCLUSIONS: There was no difference in the degree of perineal trauma after primary delivery of either the anterior or posterior shoulder. Consequently both maneuvers for shoulder delivery can be used at vaginal delivery, but further trials are warranted before certain methods can be recommended.