Mode of Vaginal Delivery: A Modifiable Intrapartum Risk Factor for Obstetric Anal Sphincter Injury

Table 1

Sultan’s classification of perineal trauma.

1st degree	Laceration of vaginal epithelium or perineal skin only
2nd degree	Involvement of the perineal muscles but not the anal sphincter
3rd degree	Disruption of the anal sphincter muscles	3a: <50% thickness of external sphincter torn
		3b: >50% thickness of external sphincter torn
		3c: internal sphincter torn
4th degree	Third degree tear with disruption of the anal epithelium as well