<prompt> Following delivery, tear involves perineum, external anal spincter with intact mucosa, grade of tear is -First degreeSecond degreeThird degreeFourth degree  <response>: Ans. is c i.e., Third degree Classification of Obstetric Anal Sphincter Injuryo First degree : Injury to perineal skino Second degree : Injury to perineum involving perineal body muscles but not involving the anal sphinctero Third degree : Injury to perineum, involving the anal sphincter complex both the external and internal. 3a: if half thickness external anal sphincter involved. 3b: if full thickness external anal sphincter involved. 3c: if internal anal sphincter involoved.o Fourth degree : Injury to perineum involving the anal sphincter complex external anal sphincter and internal anal sphincter and anal epithelium. 