Occurs when the external vaginal opening is too narrow to accomodate the baby - Leads to skin and tissues tearing as baby’s head passes

Risk factors:

• First births (nulliparity)
• Large babies (over 4kg)
• Shoulder dystocia
• Asian ethnicity
• Occipito-posterior position
• Instrumental deliveries

Classification

Perineal tears are the most common maternal obstetric injuries and can be classified into four categories:

1. First degree tear
   • Tear limited to the superficial perineal skin or vaginal mucosa only
2. Second degree tear
   • Tear extends to perineal muscles and fascia, but the anal sphincter is intact (episiotomy is anatomically classified as second degree)
3. Third degree tear
   • 3a: less than 50% of the thickness of the external anal sphincter is torn
   • 3b: more than 50% of the thickness of the external anal sphincter is torn, but the internal anal sphincter is intact
   • 3c: external and internal anal sphincters are torn, but anal mucosa is intact
4. Fourth degree tear
   • Perineal skin, muscle, anal sphincter and anal mucosa are torn

Management

The RCOG has produced guidelines suggesting the following classification of perineal tears:

• first degree
  • superficial damage with no muscle involvement
  • do not require any repair