The rate of obstetric anal sphincter injury (OASIS) is approximately 4.4% of vaginal deliveries, with 3.3% 3rd-degree tears and 1.1% 4th-degree tears.1 In the United States in 2019 there were 3,745,540 births—a 31.7% rate of cesarean delivery (CD) and a 68.3% rate of vaginal delivery—resulting in approximately 112,600 births with OASIS.2 A meta-analysis reported that, among 716,031 vaginal births, the risk factors for OASIS included: forceps delivery (relative risk [RR], 3.15), midline episiotomy (RR, 2.88), occiput posterior fetal position (RR, 2.73), vacuum delivery (RR, 2.60), Asian race (RR, 1.87), primiparity (RR, 1.59), mediolateral episiotomy (RR, 1.55), augmentation of labor (RR, 1.46), and epidural anesthesia (RR, 1.21).3 OASIS is associated with an increased risk for developing postpartum perineal pain, anal incontinence, dyspareunia, and wound breakdown.4 Complications following OASIS repair can trigger many follow-up appointments to assess wound healing and provide physical therapy.
This editorial review focuses on evolving recommendations for preventing and repairing OASIS.
The optimal cutting angle for a mediolateral episiotomy is 60 degrees from the midline
For spontaneous vaginal delivery, a policy of restricted episiotomy reduces the risk of OASIS by approximately 30%.5 With an operative vaginal delivery, especially forceps delivery of a large fetus in the occiput posterior position, a mediolateral episiotomy may help to reduce the risk of OASIS, although there are minimal data from clinical trials to support this practice. In one clinical trial, 407 women were randomly assigned to either a mediolateral or midline episiotomy.6 Approximately 25% of the births in both groups were operative deliveries. The mediolateral episiotomy began in the posterior midline of the vaginal introitus and was carried to the right side of the anal sphincter for 3 cm to 4 cm. The midline episiotomy began in the posterior midline of the vagina and was carried 2 cm to 3 cm into the midline perineal tissue. In the women having a midline or mediolateral episiotomy, a 4th-degree tear occurred in 5.5% and 0.4% of births, respectively. For the midline or mediolateral episiotomy, a third-degree tear occurred in 18.4% and 8.6%, respectively. In a prospective cohort study of 1,302 women with an episiotomy and vaginal birth, the rate of OASIS associated with midline or mediolateral episiotomy was 14.8% and 7%, respectively (P<.05).7 In this study, the operative vaginal delivery rate was 11.6% and 15.2% for the women in the midline and mediolateral groups, respectively.
The angle of the mediolateral episiotomy may influence the rate of OASIS and persistent postpartum perineal pain. In one study, 330 nulliparous women who were assessed to need a mediolateral episiotomy at delivery were randomized to an incision with a 40- or 60-degree angle from the midline.8 Prior to incision, a line was drawn on the skin to mark the course of the incision and then infiltrated with 10 mL of lignocaine. The fetal head was delivered with a Ritgen maneuver. The length of the episiotomy averaged 4 cm in both groups. After delivery, the angle of the episiotomy incision was reassessed. The episiotomy incision cut 60 degrees from the midline was measured on average to be 44 degrees from the midline after delivery of the newborn. Similarly, the incision cut at a 40-degree angle was measured to be 24 degrees from the midline after delivery. The rates of OASIS in the women who had a 40- and 60-degree angle incision were 5.5% and 2.4%, respectively (P = .16).
Continue to: Use a prophylactic antibiotic with extended coverage for anaerobes prior to or during your anal sphincter repair...