Obstetric Anal Sphincter Injuries - A Complication of Vaginal Delivery

What Are Obstetric Anal Sphincter Injuries?

Obstetric anal sphincter injuries (OASIS), also known as third and fourth-degree perineal lacerations, are complications occurred during vaginal delivery. The tears or lacerations extend from the perineum to the anus (or rectum) and include the muscles responsible for opening and closing the anus. It can often lead to morbidities like wound breakdown or perineal pain, loss of bowel control, and sexual dysfunction in women.

What Are the Primary Risk Factors for Obstetric Anal Sphincter Injuries?

The risk factors for obstetric anal sphincter injuries are as follows-

• First vaginal delivery.

• Heavy baby.

• Fetal distress or post-delivery.

• A persistent occipito-posterior position during delivery.

• Prolonged labor.

• Shoulder dystocia (when one or both shoulders of the baby get stuck during vaginal delivery).

• Midline episiotomy (incision made from the middle of the vaginal toward the anus).

• An instrumental vaginal delivery.

• Mother has weak tissue or short perineum.

• Infibulation.

• Maternal diabetes.

• Waterbirth.

What Are the Symptoms of Obstetric Anal Sphincter Injuries?

Obstetric anal sphincter injuries can significantly impact women by impairing their quality of life. The following symptoms can be noticed after an OASIS injury -

• Perineal pain.

• Edema and bruising due to tight sutures, infection, or wound breakdown.

• Urinary retention and defecation problems in the postpartum period.

• Dyspareunia (genital pain before, during, or after sexual intercourse).

• Altered sexual function.

• In severe cases - abscess formation wound breakdown, and rectovaginal fistulae formation.

• Anal incontinence and anorectal symptoms.

How Are Obstetric Anal Sphincter Injuries Classified?

Perineal tears that occur commonly during vaginal birth are graded based on severity as-

1. Grade 1 - Injury to perineal skin only.

2. Grade 2 - Injury to the perineum involving perineal muscles (not the anal sphincter).

3. Grade 3 (through external anal sphincter muscle).

• 3a - Less than 50 % of external anal sphincter thickness torn.

• 3b - More than 50 % of external anal sphincter thickness torn.

• 3c - Both external and internal anal sphincter torn.

4. Grade 4 - Injury to the perineum involving the anal sphincter complex and anal epithelium.

The first-grade and second-grade injuries usually do not require any intense reparative surgery. Instead, the doctors can simply suture the area on the delivery table. As a result, the healing and postoperative outcomes are primarily good.

The third-grade and fourth-grade perineal tears are obstetric anal sphincter injuries. They are more severe injuries and require reparative surgery.

How to Prevent Obstetric Anal Sphincter Injuries?

During delivery, sometimes it becomes impossible to avoid obstetric anal sphincter injuries due to the circumstances, but the following measures can be taken to prevent obstetric anal sphincter injuries-

• Head Control - Slowing down the delivery of the head and using only the uterine expulsive efforts.

• Perineal Support - Application of warm compresses to the perineum and intrapartum perineal massage.

• Delivery position.

• Episiotomy - Restricted use of episiotomy is preferable in women having a spontaneous vaginal delivery.

• Other Factors - Antepartum perineal massage, pushing position, open versus closed glottis pushing, Ritgen’s maneuver, water birth, and delayed pushing (in women with epidural) do not show any protective effect on the anal canal.

• Commencing perineal massage from 35 weeks of the pregnancy.

What Is the Management of Obstetric Anal Sphincter Injuries?

• In the delivery or operating room, obstetric anal sphincter injuries repairs are carried out in the delivery room or the operating room.

• It can be commonly repaired under local anesthetic, general or regional anesthesia.

• Sutures - After analyzing the severity, location, and depth of injury, stitches are placed by the doctors to repair the tear. Sutures can be absorbable as well as non-absorbabe.

• Repair of the Anal Mucosa - The mucosal repair can be carried out with an interrupted vicryl suture or continuous submucosal suture.

• Repair of the External and Internal Anal Sphincters - Suturing is done by either end-to-end repair or overlap repair techniques. The procedure is also known as sphincteroplasty (sphincter repair).

• Women with anal incontinence following OASIS should be referred for pelvic floor physiotherapy.

What to Expect After Repair of Obstetric Anal Sphincter Injuries?

• Prophylactic Antibiotics - After the procedure, the doctor will prescribe antibiotics to prevent infections and postpartum perineal wound complications. Second-generation Cephalosporins are usually prescribed.

• Postoperative Bowel Regimen - It varies from patient to patient. It consists of laxatives and bulking agents to avoid constipation and any damage to the repaired tissues from the passage of hard stool. The bowel motions in the immediate postoperative period may threaten the integrity of the repair, so bowel confinement techniques are used.

• Postoperative Analgesia - To relieve perineal pain due to trauma. As Opioids have a constipating effect, NSAIDs (nonsteroidal anti-inflammatory drugs) in conjunction with Acetaminophen are preferred.

• Bladder Catheterization - Perineal trauma and postpartum urinary retention are closely associated.

Is It Possible to Have a Normal Vaginal Delivery After Obstetric Anal Sphincter Injuries?

Experiencing an obstetric anal sphincter injury during one delivery does not imply that it will happen again during future deliveries. After a successful repair surgery of obstetrical anal sphincter injuries, most women can safely deliver the baby vaginally in a future pregnancy. However, the doctor may suggest a cesarean section (C-section) delivery to prevent future obstetric anal sphincter injuries.

Conclusion

Obstetric anal sphincter injuries are a significant cause of morbidity after vaginal delivery. Few measures can be taken during delivery to diminish the risk of occurrence. Careful examination after every delivery is vital to avoid missing an obstetric anal sphincter injury (OASIS). A close follow-up should be scheduled after the systematic repair of the entire anal sphincter complex. Most women following OASIS can have a vaginal delivery. Post-delivery evaluation of symptoms and anal function testing can help guide the choice of a future mode of delivery.