Problem: The perineal-bundle is a complex intervention widely implemented in Australian maternity care facilities. Background: Most bundle components have limited or conflicting evidence and the implementation required many midwives to change their usual practice for preventing perineal trauma. Aim: To measure the effect of perineal bundle implementation on perineal injury for women having unassisted births with midwives. Methods: A retrospective pre-post implementation study design to determine rates of second degree, severe perineal trauma, and episiotomy. Women who had an unassisted, singleton, cephalic vaginal birth at term between two time periods: January 2011 – November 2017 and August 2018 – August 2020 with a midwife or midwifery student accoucheur. We conducted logistic regression on the primary outcomes to control for confounding variables. Findings: data from 20,155 births (pre-implementation) and 6273 (post-implementation) were analysed. After implementation, no significant difference in likelihood of severe perineal trauma was demonstrated (aOR 0.86, 95% CI 0.71–1.04, p = 0.124). Nulliparous women were more likely to receive an episiotomy (aOR 1.49 95% CI 1.31–1.70 p < 0.001) and multiparous women to suffer a second degree tear (aOR 1.18 95% CI 1.09–1.27 p < 0.001). Discussion: This study adds to the growing body of literature which suggests a number of bundle components are ineffective, and some potentially harmful. Why, and how, the bundle was introduced at scale without a research framework to test efficacy and safety is a key concern. Conclusion: Suitably designed trials should be undertaken on all proposed individual or grouped perineal protection strategies prior to broad adoption.