In simple words: This code describes a tear during childbirth that goes through the skin and muscles between the vagina and anus, and also involves a small tear in the muscle that controls the anus (less than 50% of the muscle thickness).

Third-degree perineal laceration during delivery, IIIa.A third-degree perineal laceration extends through the vaginal epithelium and perineal skin, as well as the perineal muscles and extends into the external anal sphincter (EAS).IIIa indicates that less than 50% of the EAS thickness is torn.

Example 1: A 28-year-old woman delivers vaginally, and upon examination, the physician notes a perineal laceration extending through the skin, muscles, and less than 50% of the external anal sphincter. This is coded as O70.21., A 35-year-old woman with a history of prior episiotomy delivers vaginally.During the delivery, she sustains a third-degree perineal laceration, involving less than half of the external anal sphincter thickness, along with an extension of the prior episiotomy. The appropriate code is O70.21., A patient delivers a large infant and sustains a tear involving the skin, perineal muscles, and less than 50% of the external anal sphincter. The physician repairs the laceration. O70.21 is the appropriate code.

Documentation should clearly specify the degree of the laceration, the extent of the anal sphincter involvement (less than 50% tear), and any associated injuries. Operative reports should detail the repair of the laceration.

** This code is specifically for third-degree perineal lacerations involving *less than 50%* of the EAS thickness.Other codes exist for different levels of EAS or rectal mucosa involvement.