Which practices reduce risk of anal sphincter injury and preserve bowel function?
Executive summary
A range of prevention practices—manual perineal protection, controlled delivery of the fetal head (fetal head flexion and control), and selective mediolateral episiotomy—are consistently recommended in recent guidelines and cohort reports to reduce obstetric anal sphincter injuries (OASIS) and thereby help preserve bowel function [1] [2] [3]. Care bundles that combine antenatal education, hands‑on perineal protection, selective episiotomy when indicated, and routine perineal/rectal examination after vaginal birth have been implemented in multiple countries and are associated with reduced OASIS rates or are recommended by guideline groups [3] [4] [5].
1. Hands-on perineal protection: the frontline maneuver
Manual perineal protection—supporting the perineum and controlling the head as it crowns—is a central element of care bundles deployed to prevent OASIS; Norway’s national bundle launched in 2005 that included manual protection is explicitly linked to national efforts to reduce recurrence of sphincter injuries [3]. Reviews and practice guidelines identify perineal techniques during second stage labour, such as controlled delivery of the head, as associated with lower rates of severe tears [6] [2].
2. Controlled fetal head flexion and controlled delivery: evidence and rationale
“Fetal head flexion and control” (slowing and supporting the head to avoid sudden expulsive forces) is cited repeatedly as a prevention strategy associated with fewer sphincter injuries in recent guideline summaries and reviews [2] [1]. The proposed mechanism is that controlled descent reduces extreme stretching and sudden tearing of the perineum; national guideline reviews and systematic reviews list this among the measures linked to reduced OASIS [7] [2].
3. Episiotomy: selective mediolateral use, not routine
Major guideline sources and reviews make two linked points: routine episiotomy is not recommended, but a mediolateral episiotomy (angled 45–60° from midline) in indicated situations—especially instrumental deliveries—can lower sphincter injury risk compared with spontaneous severe lacerations [8] [1]. Authors and guideline panels therefore advocate selective, correctly angled mediolateral episiotomy rather than routine cutting [8] [1].
4. Care bundles and structured protocols: system-level effects
Several countries have implemented standardized care bundles (antenatal education, perineal protection, selective episiotomy, structured examination after delivery) and guideline No. 457 and other national documents promote such bundles to improve recognition, prevention and outcomes [4] [1] [5]. Cohort and implementation studies from Nordic countries and institutional audits have linked bundles—including manual protection—to reductions in OASIS rates or improved detection, although results vary by setting [3] [9].
5. Training, detection and repair: prevention’s necessary partners
Prevention is only one part of preserving function; guideline authors stress training in both prevention and prompt diagnosis/repair (including routine perineal and rectal exam after vaginal delivery) because missed or unrepaired OASIS leads to worse continence outcomes [10] [1]. Systematic efforts to train staff in repair techniques and to standardize classification are recommended to limit long‑term bowel dysfunction after an injury [11] [1].
6. Tradeoffs, remaining uncertainty and differing interpretations
There is consensus on core elements (protection, controlled delivery, selective mediolateral episiotomy, training), but the literature and guidelines note variation in methodological quality and outcomes across studies and countries; some implementations did not show significant decreases in overall OASIS in every setting [7] [4]. The role of episiotomy remains debated—guidelines settle on selective mediolateral use when indicated rather than routine use because evidence and risks vary by population and obstetric context [8] [1].
7. Practical takeaway for counselling and clinical decisions
For patients and clinicians aiming to reduce sphincter injury risk and preserve bowel function, available guideline guidance supports use of perineal protection and controlled delivery techniques, selective mediolateral episiotomy in indicated cases (especially instrumental deliveries), and ensuring experienced staff and immediate postpartum examination and repair if OASIS occurs [2] [8] [1]. Decisions about mode of birth after prior OASIS and individualized counselling are addressed in recent reviews; women with prior OASIS face higher recurrence risk and should receive evidence‑based counselling per updated reviews and guideline summaries [12] [5].
Limitations: available sources emphasize prevention bundles and guideline recommendations and report cohort/implementation data; randomized trial evidence for individual components is limited in the provided set and some guideline panels note variable methodological quality and inconsistent outcomes across settings [7] [4].