Levator ani muscle avulsion (LAMA) is a major obstetric injury affecting 10-36% of vaginally parous women, with significant long-term sequelae including pelvic organ prolapse (POP) and stress urinary incontinence (SUI). LAMA disrupts the structural integrity of the pelvic floor, causing bladder neck hypermobility and compromising urethral support mechanisms essential for continence. The avulsed levator ani loses its ability to compress the urethra against the pubic symphysis during increased intra-abdominal pressure, predisposing to SUI. While mode of delivery is recognized as the primary modifiable risk factor, comprehensive quantitative synthesis across delivery modes remains incomplete. This systematic review and meta-analysis aimed to determine pooled LAMA prevalence stratified by delivery mode and quantify comparative risk between modes using standardized imaging criteria.

We systematically searched PubMed, Embase, Scopus, CINAHL, and Cochrane Library from January 2000 through December 2025 using terms: "levator ani," "levator avulsion," "levator trauma," combined with "delivery mode," "forceps," "vacuum," "cesarean," and "ultrasound" or "MRI". 
Inclusion criteria required: (1) LAMA confirmed by transperineal ultrasound (TPUS) or MRI using standardized criteria (≥3 of 4 insertion points detached on tomographic ultrasound imaging or equivalent MRI findings),with defined delivery mode-specific prevalence data, Pariety. Two independent reviewers performed screening, data extraction, and quality. Pooled prevalence estimates were calculated. Most studies were prospective cohorts from specialized urogynaecology centers, with TPUS performed 3-12 months postpartum. Significant heterogeneity existed across studies due to variations in imaging protocols, operator experience, and population characteristics.

Most studies were prospective cohorts from specialized urogynaecology centers, with transperineal ultrasound performed 3–12 months postpartum. Significant heterogeneity existed across studies due to variations in imaging protocols, operator experience, and population characteristics. Pooled prevalence demonstrated a clear risk gradient: elective cesarean section showed minimal rates, spontaneous vaginal delivery exhibited low-to-moderate prevalence, vacuum extraction showed moderately elevated rates, forceps delivery demonstrated substantially higher prevalence, and sequential instrumental delivery exhibited the highest rates.

Compared with spontaneous vaginal delivery, forceps delivery demonstrated four-fold increased risk, vacuum extraction showed two-fold increased risk, and sequential instrumental delivery carried six-fold increased risk. Forceps conferred approximately two-and-a-half-fold higher risk than vacuum extraction. Rotational forceps demonstrated significantly higher prevalence than non-rotational forceps. Mediolateral episiotomy showed potential protective effect in forceps deliveries. Prolonged second stage increased risk in spontaneous vaginal delivery. Magnetic resonance imaging detected slightly more avulsions than transperineal ultrasound, particularly partial avulsions.

This meta-analysis confirms mode of delivery as the principal determinant of levator ani muscle avulsion, with a clear risk gradient from elective cesarean to sequential instrumental delivery. Forceps delivery, particularly rotational techniques, emerges as the strongest modifiable risk factor, consistent with International Urogynecological Association and International Continence Society terminology on obstetric pelvic floor trauma. The biomechanical basis is compelling: forceps application creates direct compression and stretching forces on the levator ani during blade insertion and traction, particularly during rotation maneuvers, rendering the pubococcygeus insertion at the pubic bone especially vulnerable to injury.

Mode of delivery represents the primary modifiable determinant of levator ani muscle avulsion, with forceps delivery especially rotational techniques conferring 4-fold higher risk compared with spontaneous vaginal delivery. The substantial prevalence even after uncomplicated vaginal birth (13-36%) underscores the inherent vulnerability of levator structures during parturition. These findings support judicious use of operative vaginal delivery, optimization of operator training, consideration of protective episiotomy techniques, and informed counseling regarding delivery mode and long-term pelvic floor health. Future research should prioritize standardized imaging protocols, long-term functional outcome assessment, and evaluation of preventive intrapartum strategies through adequately powered randomized trials.

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Continence 19S (2026) 102537
DOI: 10.1016/j.cont.2026.102537