Table 1.

Classification of perineal trauma

First degree:	Injury to skin only
Second degree:	Injury to the perineum involving perineal muscles but not involving the anal sphincter
Third degree:	Injury to the perineum involving the anal sphincter complex; 3a < 50% of external anal sphincter (EAS) thickness torn; 3b > 50% of EAS thickness torn; 3c Internal anal sphincter (IAS) torn
Fourth degree:	Injury to perineum involving the anal sphincter complex (EAS and/or IAS) and anal epithelium

RCOG Green Top Guideline 23. Methods and Materials Used in Perineal Repair. Kettle C, O'Brien PMS.