TOPLINE

The extension of the hips directed at crowning during vaginal birth was not associated with a reduction in the rate of second-degree or higher perineal lacerations compared with usual flexed positioning among patients delivering for the first time. However, ordinal analyses suggested that the extension of the hips shifted the distribution of perineal trauma and was associated with reduced odds of higher-order lacerations.

METHODOLOGY

• Researchers conducted a randomized controlled trial (April 2021 to July 2025) at a tertiary care center in Boston to determine how the extension of the hips at crowning affects significant perineal lacerations during vaginal delivery.
• They included 1206 adult first-time mothers (median age, 32 years) carrying singleton, vertex, nonanomalous fetuses at term and undergoing vaginal delivery.
• At complete cervical dilation, participants were randomly assigned to either the usual care group (typically with the hips flexed; n = 613) or the intervention group (instructed to lower the legs and extend the hips just before crowning; n = 593).
• Significant perineal lacerations — comprising second-, third-, or fourth-degree lacerations — served as the primary outcome.
• Researchers also assessed the rates of obstetric anal sphincter injuries, postpartum vaginal pain, perineal lacerations (ordinal outcome), and other outcomes. Analyses were conducted on both intention-to-treat and as-treated bases, with adjustments for various factors.

TAKEAWAY

• The incidence of significant perineal lacerations did not differ significantly between the usual care and intervention groups (66.2% vs 66.6%; P = .89), and rates of obstetric anal sphincter injuries were similar (8.0% vs 8.3%; P = .86).
• Among participants assigned to the intervention group, 25% delivered with their hips flexed rather than extended; these patients were more likely to have a longer second stage of labor (116 vs 81 minutes; P < .001) and undergo operative deliveries (P for distribution < .001).
• In as-treated analyses, the extension of the hips was linked to lower rates of significant perineal lacerations (62.7% vs 68.7%; P = .03) and obstetric anal sphincter injuries (5.2% vs 9.9%; P = .004) than flexed positioning; however, these differences were not significant in the adjusted analysis.
• The ordinal analysis of perineal lacerations in the as-treated cohort demonstrated a protective effect with the extension of the hips, which was associated with reduced odds of higher-order lacerations (adjusted odds ratio, 0.77; P = .03).

IN PRACTICE

"Our 'true positioning' rather than 'expected positioning' data suggest barriers to implementation of the intervention, especially among patients with these labor characteristics," the authors wrote. "It is possible that with a larger sample size, greater positioning adherence, and restriction to spontaneous deliveries, this repositioning maneuver could benefit nulliparous patients," they added.

SOURCE

The study was led by Marti D. Soffer, MD, MPH, of the Department of Obstetrics and Gynecology at Massachusetts General Hospital in Boston. It was published online on September 22, 2026, in Obstetrics & Gynecology.

LIMITATIONS

A notable proportion of participants assigned to the intervention deviated from the assignment and delivered with hips flexed rather than extended. The study population may not be representative of all birthing centers, thereby limiting generalizability. The impact of estimated fetal weight on positioning-related clinical decision-making could not be established.

DISCLOSURES

The study received partial support through an internal sundry fund. One author disclosed consulting for Roon.com; another author reported receiving funding from the Patient-Centered Outcomes Research Institute and the National Institutes of Health; and a third author reported a medical advisory board role with equity in Delfina Health, receiving a stipend from the American College of Obstetricians and Gynecologists for editorial services, receiving grant funding from the National Heart, Lung, and Blood Institute and Massachusetts Institute of Technology, and having other ties, all outside the scope of this work.

This article was created using several editorial tools, including AI, as part of the process. Human editors reviewed this content before publication.