Effect of Hip Extension Compared With Usual Positioning on Perineal Lacerations During First Vaginal Delivery: A Randomized Clinical Trial.

OBJECTIVE: To determine the effect of hip extension at the time of crowning on perineal lacerations and obstetric anal sphincter injuries. METHODS: This was a randomized, pragmatic, nonblinded clinical trial. Participants included nulliparous patients aged 18 years or older with singleton term gestations with nonanomalous fetuses. Immediately before crowning, participants in the intervention group were directed to lower their legs, extending the angle of their hips. Participants in the usual care group were undirected and typically delivered in the flexed position. The primary outcome was a composite of significant perineal lacerations, defined as second-degree, third-degree, or fourth-degree lacerations. Secondary outcomes included the rates of obstetric anal sphincter injuries and perineal lacerations as an ordinal outcome. Analyses were planned on intention-to-treat (ITT) and as-treated bases. RESULTS: In total, 1,206 participants delivered vaginally after randomization. The primary composite of significant perineal lacerations was not significantly different in the ITT analysis (66.2% usual care vs 66.6% intervention, P=.89). Twenty-five percent of those randomized to the intervention were not adherent. In unadjusted as-treated analyses, lower rates of significant perineal lacerations (62.7% extension vs 68.7% flexion, P=.03) and obstetric anal sphincter injuries (5.2% extension vs 9.9% flexion, P=.004) were observed; these differences were not significant after adjustments. Ordinal comparison of lacerations in the as-treated analysis demonstrated a protective shift in the laceration distribution curve, with more intact perineums and fewer obstetric anal sphincter injuries among those in the extension group (unadjusted P=.006, adjusted P=.03). CONCLUSION: Extension of the hips did not reduce significant perineal lacerations at the time of term vaginal delivery in nulliparous patients. CLINICAL TRIAL REGISTRATION: ClinicalTrials.gov, NCT04616170.