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Updated: May 24, 2026
03:49
Anogenital Distance and Perineal Measurements of the Pelvic Organ Prolapse (POP) Quantification System
Published on: September 20, 2018
Episiotomy characteristics and risks for obstetric anal sphincter injuries: a case-control study
M Stedenfeldt1, J Pirhonen, E Blix
1The Norwegian Continence and Pelvic Floor Centre, University Hospital of North Norway, Tromsø, Norway. mona.stedenfeldt@unn.no
Summary
Deeper, longer episiotomies and those incised further from the midline reduce the risk of obstetric anal sphincter injuries (OASIS). Angles between 30-60° are also associated with fewer OASIS, while very acute or wide angles increase risk.
Area of Science:
- Obstetrics and Gynecology
- Surgical Anatomy
- Pelvic Floor Disorders
Background:
- Obstetric anal sphincter injuries (OASIS) are a significant complication of vaginal birth.
- Episiotomy, a surgical incision, is sometimes performed to facilitate delivery.
- The geometrical properties of episiotomies may influence the risk of OASIS.
Purpose of the Study:
- To investigate the association between episiotomy geometry and the occurrence of OASIS.
- To identify specific episiotomy characteristics that may mitigate OASIS risk.
Main Methods:
- A case-control study was conducted comparing women with OASIS (cases) and without OASIS (controls).
- Episiotomy scars were measured for angle, length, depth, and incision point.
- Conditional logistic analysis was used to analyze the data.
Main Results:
- Increased episiotomy depth, length, and distance of incision from the midline were associated with a significantly reduced risk of OASIS.
- A U-shaped association was observed for episiotomy angle, with increased OASIS risk at angles <15° or >60°.
- Optimal episiotomy dimensions for reduced OASIS risk were depth >16 mm, length >17 mm, and incision point >9 mm lateral of the midpoint.
Conclusions:
- Episiotomy dimensions, including depth, length, and incision location, are critical factors in preventing OASIS.
- An episiotomy angle between 30-60° is associated with a lower risk of OASIS.
- Tissue shrinkage during healing should be considered when evaluating episiotomy geometry.
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