(perineal trauma) an injury to the perineum, which may be sustained during childbirth. Perineal tears can be classified by degree. First-degree tears involve the perineal skin and vaginal mucosa only. Second-degree tears involve the perineal muscles but not the anal sphincter. Third-degree tears involve the anal sphincter complex: the external anal sphincter (EAS) and internal anal sphincter (IAS). These are subclassified as 3a (less than 50% of EAS thickness torn), 3b (more than 50% of EAS thickness torn), and 3c (IAS torn). Fourth-degree tears involve the anal sphincter complex (EAS and IAS) and the anal epithelium or rectal mucosa. It is vitally important that these injuries are recognized and repaired by competent personnel. See also obstetric anal sphincter injury.
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