Classification of obstetric lacerations^[1]

First degree

Injury to perineal skin only

Second degree

Injury to perineum involving perineal muscles but not involving anal sphincter

Third degree

Injury to perineum involving anal sphincter complex

3a: Less than 50% of external anal sphincter thickness torn

3b: More than 50% external anal sphincter thickness torn

3c: Both external anal sphincter and internal anal sphincter torn

Fourth degree

Injury to perineum involving anal sphincter complex (external anal sphincter and internal anal sphincter) and anal epithelium

Reference:

Graphic 116249 Version 3.0

Classification of obstetric lacerations[1]