Classifications and Management of Obstetric Perineal Injuries
Classification System
Obstetric perineal injuries are classified into four degrees based on the ACOG reVITALize standardized definitions, with third- and fourth-degree tears (OASIS) requiring the most intensive management due to their association with long-term anal incontinence in 35-60% of women. 1
Degree-by-Degree Classification:
First-degree: Injury to perineal skin or vaginal mucosa only, without involvement of underlying muscle 1
Second-degree: Injury involving perineal skin, vaginal epithelium, and perineal body musculature (bulbocavernosus and transverse perineal muscles), but not the anal sphincter 1
Third-degree (OASIS): Injury involving the anal sphincter complex 1, 2
- 3a: Less than 50% of external anal sphincter (EAS) thickness torn
- 3b: More than 50% of EAS thickness torn
- 3c: Both EAS and internal anal sphincter (IAS) torn
Fourth-degree (OASIS): Injury extending through the anal sphincter complex and anorectal mucosa 1, 2
Critical distinction: OASIS with isolated EAS involvement (3a/3b) has better functional prognosis than injuries affecting the IAS or anorectal mucosa (3c/4), though prevalence of anorectal symptoms increases with severity 2
Diagnostic Approach
After every vaginal delivery, perform systematic evaluation including visual inspection, thorough perineal examination, and digital rectal examination—the rectal exam is mandatory as it significantly improves OASIS detection rates. 1
Key Diagnostic Steps:
Adequate lighting and patient positioning are essential before examination 1
Digital rectal examination must be performed after all vaginal deliveries to detect occult sphincter injuries 1
No routine imaging needed: Clinical examination by a knowledgeable provider is equivalent to endoanal ultrasound for immediate post-delivery OASIS detection 1
When uncertain: Obtain a second experienced examiner to confirm the degree of injury 1
Delayed repair is acceptable: If the primary surgeon is inexperienced, pack the wound and delay repair 8-12 hours until an experienced provider is available 1
Management by Injury Degree
First-Degree Lacerations
For hemostatic first-degree tears, use skin adhesive or no suturing rather than traditional suturing—these methods reduce pain, procedure time, and achieve equivalent functional outcomes. 1
Management options (in order of preference):
No suturing if hemostatic—associated with less pain and similar healing 1
Skin adhesive (octyl cyanoacrylate):
Suturing only if above methods inadequate 1
Second-Degree Lacerations and Episiotomies
For second-degree tears, if hemostatic, use skin adhesive or no suturing for the perineal skin after repairing deeper layers—this reduces pain, dyspareunia, and improves breastfeeding rates at 3 months. 1
Surgical Technique (when suturing required):
Prepare the field: Betadine or chlorhexidine preparation 1
Ensure adequate analgesia: Local infiltration or regional anesthesia 1
Repair sequence:
- Anchor suture above the vaginal apex 1
- Close vaginal epithelium, muscularis, and rectovaginal fascia with continuous non-locking suture to the hymenal ring 1
- Transition to axial plane and reapproximate bulbocavernosus and transverse perineal muscles in continuous, non-locking fashion 1
- For perineal skin: Use continuous non-locking subcuticular technique OR skin adhesive OR leave unsutured 1
- Anchor final knot behind the hymen 1
Suture selection: Absorbable synthetic sutures (polyglycolic acid or polyglactin) with continuous non-locking technique 1
Avoid: Transcutaneous interrupted sutures—they damage nerve endings and increase pain 1
Third- and Fourth-Degree Lacerations (OASIS)
OASIS repairs require regional or general anesthesia, antibiotic prophylaxis, and use of a surgical checklist to ensure adherence to critical care processes and reduce errors. 1
Pre-operative Requirements:
Anesthesia: Regional or general (not local) 1
Setting: Operating room preferred for optimal visualization and exposure 1
Antibiotic prophylaxis (mandatory): 1
- First-generation cephalosporin: Cefazolin 2g, OR
- Second-generation cephalosporin: Cefoxitin 2g, OR
- If penicillin allergic: Gentamicin 5 mg/kg + Clindamycin 900 mg + Metronidazole 500 mg
Vaginal preparation: Povidone-iodine or chlorhexidine 1
Surgical count: Count instruments, sponges, and sutures pre- and post-operatively 1
Post-operative Care (Critical for Outcomes):
Stool softeners (mandatory): Polyethylene glycol 4450 or mineral oil twice daily for 6 weeks to achieve toothpaste-consistency stools 1
Pain control: Acetaminophen, ibuprofen, ice packs; opiates only if needed 1
Sitz baths: Twice daily until first wound check 1
Early follow-up: Within 2 weeks, ideally in specialized postpartum perineal clinic 1
Patient education: Clear documentation and discussion of injury degree 1
If concern for sphincter compromise: Perform endoanal ultrasound to assess full extent of damage 1
Common Pitfalls and How to Avoid Them
Missed OASIS diagnosis is the most critical error—always perform digital rectal examination after every vaginal delivery, regardless of visible perineal trauma. 1
Key Pitfalls:
Inadequate examination lighting: Ensure optimal visualization before declaring injury degree 1
Skipping rectal exam: This is the primary cause of missed OASIS 1
Inexperienced primary surgeon: If uncertain, delay repair 8-12 hours for experienced provider rather than performing inadequate repair 1
Using locking sutures: Causes excessive tension, tissue edema, and necrosis—always use non-locking continuous technique 1
Transcutaneous skin sutures: Damage nerve endings and increase pain—use subcuticular technique instead 1
Inadequate anesthesia for OASIS: Local anesthesia is insufficient; use regional or general 1
Forgetting stool softeners: Failure to prescribe 6-week course significantly increases wound complications 1
Prevalence Context
- First-degree: 5.5-16.4% of vaginal births 1
- Second-degree: 29.0-35.1% of vaginal births 1
- Third-degree: 1.8-7.1% of vaginal births (3.3% average) 1
- Fourth-degree: 0-0.3% of vaginal births (1.1% average) 1
Risk is higher in nulliparous women (1.4-16% OASIS rate) versus multiparous (0.4-2.7%), with recurrence risk of 5.1-10.7% in women with prior OASIS. 2