Perineal Trauma and Obstetric Anal Sphincter Injuries (OASIs) in the United Kingdom: National Trends and Practice Changes Over a Decade.

INTRODUCTION AND HYPOTHESIS: OASIs affect 6.1% of primiparous and 1.7% of multiparous women in the UK. However, rates of OASI increased threefold between 2000 and 2012. This study aimed firstly to evaluate the current incidence and management of perineal trauma, including mode of birth, OASI and episiotomy in UK maternity units and secondly to monitor temporal trends since the previous national survey.

METHODS

Freedom of information requests were sent to all UK maternity units requesting data on births between January 2024 and January 2025. Data from the 2009-2010 survey were re-analysed to compare the OASI, episiotomy, operative vaginal birth, and cesarean section (CS) rates at both time points.

RESULTS

One hundred sixty-one of 268 units (59.7%) responded, including 469,744 births (78.9% of the total births). The median OASI rate was 3.1% (0-12.5%), affecting 6.4% of primiparous women and 1.2% of multiparous women (p < 0.001). Between 2009 and 2025, the odds of a forceps-assisted birth (OR 1.07 [95% CI 1.04-1.09]), OASI (OR 1.15 [95% CI 1.05-1.28]), and CS (OR 1.07 [95% CI 1.04-1.09]) increased in primiparous women. In multiparous women, the rate of CS alone increased (OR 1.04 [95% CI 1.02-1.06]). Overall, there was no change in vacuum-assisted births or episiotomy rates.

CONCLUSIONS

This survey provides an update of the incidence of OASI in the UK, identifying an increase in forceps use and OASI incidence in primiparous women. This supports the need for further targeted strategies to reduce OASI, including enhanced training and support for vacuum-assisted births, and appropriate use of mediolateral episiotomy with forceps-assisted births.