Premature Rupture of Membranes

Trauma to the perineum occurring during vaginal delivery, classified by degree: first degree (skin only), second degree (perineal muscle involved, not the anal sphincter, the most common significant tear), third degree (involving the anal sphincter complex, further subdivided 3a, less than 50% external anal sphincter thickness torn; 3b, more than 50% torn; 3c, internal anal sphincter also torn), and fourth degree (extending through the anal sphincter complex into the rectal mucosa).

Third and fourth degree tears are collectively termed obstetric anal sphincter injuries (OASIS).

Risk factors include nulliparity, instrumental delivery (particularly forceps), macrosomia, occipito-posterior position, prolonged second stage, and shoulder dystocia.

Visible perineal trauma at delivery; third and fourth degree tears may not always be immediately obvious on visual inspection alone and require careful, systematic examination to identify.

Systematic examination after every vaginal delivery, including a rectal examination, is essential to correctly classify the degree of tear and specifically assess for sphincter involvement, given the significant consequences of a missed OASIS for long-term continence.

• First and second degree tears: repaired under local anesthesia (or existing regional analgesia) using absorbable suture material, with a continuous, non-locked technique for the perineal skin generally associated with less short-term pain than interrupted sutures
• Third and fourth degree tears (OASIS) require repair in theatre under regional or general anesthesia by an appropriately trained practitioner, given the technical demands of sphincter repair: the torn sphincter ends are identified and repaired (commonly using an end-to-end or overlap technique for the external anal sphincter), with the internal sphincter, if torn, repaired separately, and the rectal mucosa (fourth degree) closed first
• Broad-spectrum prophylactic antibiotics are given at the time of OASIS repair (commonly a single dose or short course, e.g. IV co-amoxiclav or cefuroxime plus metronidazole), given evidence this reduces wound infection and breakdown risk
• Laxatives (a stool softener such as lactulose, often combined with a bulking agent) are routinely prescribed after OASIS repair to reduce straining and protect the repair
• Analgesia (regular paracetamol and NSAIDs, with opioids as needed), and physiotherapy input for pelvic floor exercises
• Follow-up at 6 to 12 weeks in a dedicated perineal clinic after OASIS, assessing continence and wound healing, with endoanal ultrasound and anorectal manometry available where symptoms of incontinence or urgency persist
• Counseling regarding mode of delivery in a subsequent pregnancy after OASIS is individualized, with the option of elective cesarean discussed, particularly if the woman remains symptomatic

Referral: appropriately trained obstetrician for repair of any third or fourth degree tear; dedicated perineal clinic follow-up after OASIS; colorectal surgery for persistent, significant incontinence despite conservative management.