Hip extension during delivery might result in fewer perineal lacerations or anal sphincter injuries, based on data presented at the Society for Maternal-Fetal Medicine (SMFM) 2026 Annual Pregnancy Meeting in Las Vegas.
Although similarities in adverse outcomes between the intervention and usual care in the intent-to-treat analysis were not statistically significant, if pregnant patients had adhered to the intervention, fewer lacerations would have occurred, as reported in a secondary as-treated analysis with significant results.
The results support the intervention for patients undergoing their first vaginal delivery, said Marti D. Soffer, MD, MPH, OB/GYN and maternal-fetal medicine specialist at Massachusetts General Hospital in Boston, who led the study.
“Extending the hips at the time of delivery among nulliparous patients didn’t show a benefit in preventing significant perineal lacerations, though the as-treated analyses suggested a benefit for low-risk deliveries,” Soffer said.
- Nulliparous vaginal delivery: hip extension at crowning showed no ITT benefit.
- Perineal lacerations ≈ two thirds in both groups; P = .99.
- Anal sphincter injury rates ~8% in both groups; P = .88.
- 25.4% assigned intervention did not achieve hip extension.
- As-treated analysis: ↓ laceration 69% vs 62%; ↓ sphincter injury 9.9% vs 5.3%.
Soffer and colleagues randomly assigned 1207 nulliparous patients who delivered vaginally to usual care (n = 612) or the positioning intervention (n = 595). The study included mainly patients who underwent an epidural.
The usual care group received no specific direction about leg position, which usually resulted in flexed hips, Soffer and colleagues noted. The intervention entailed directing patients to extend their hips at the time of crowning and delivery of the baby’s head.
In the intent-to-treat analysis, rates of perineal laceration were similar between the intervention and usual care groups, occurring in two thirds of both patient populations (P = .99). Rates of sphincter injury were nearly identical at a little over 8% in both groups (P = .88).
However, 25.4% of those in the intervention group did not deliver with hip extension for various reasons, including a longer second stage of labor and operative vaginal delivery.
In the secondary as-treated analysis, rates of perineal laceration in the intervention and usual care groups were 69% and 62% (P = .02), while rates of anal sphincter injury were 9.9% and 5.3% (P = .004), respectively. The effect of the intervention on both outcomes was consistent after adjusting for birthweight, episiotomy, and time spent in the second stage of labor.
Although Soffer said they expected many patients to deviate from the intervention assignment of lowering the legs at the time of crowning, the deviation rate of 25% was higher than expected, Soffer told Medscape Medical News.
Every Bit Helps
Perineal and sphincter trauma are known consequences of vaginal delivery, especially among patients delivering their first child, said Aleksandr M. Fuks, MD, professor and chair of the Department of Obstetrics & Gynecology at East Tennessee State University in Johnson City, Tennessee.
The difference in outcomes of the intent-to-treat analysis and the as-treated analysis is common in intervention studies, said Fuks, who was not involved in the research.
Additional research is needed to compare the need for instrumental vaginal delivery and cesarean sections in cases where the fetal head fails to descend during the second stage of labor between intervention and nonintervention groups of nulliparous patients, Fuks said.