Uterine Scar Dehiscence

Uterine scar dehiscence is partial separation of an old uterine scar in which the muscle layer has opened but the serosa (peritoneal covering) is intact and the membranes have not ruptured. It is often silent. It matters because it can progress to complete rupture with haemorrhage and fetal death, so any pain, bleeding or heart rate change in a woman with a scar needs immediate assessment.

• Risk factors: previous classical or T shaped scar, short interval between births, labour induction, oxytocin augmentation, scar infection, previous multiple caesareans, uterine overdistension.
• Often found incidentally at repeat caesarean section.
• Ultrasound may show a thin scar in late pregnancy.

Many women have no symptoms. Others have scar tenderness, mild persistent lower abdominal pain, light vaginal bleeding or a fetal heart rate abnormality in labour.

• Localised tenderness over the scar.
• Haematuria or small amounts of bleeding may occur.
• Differential diagnosis: normal scar pain, uterine rupture, placental abruption, urinary infection, labour contractions, round ligament pain.
• Complications: progression to uterine rupture, haemorrhage, fetal distress, preterm birth, hysterectomy, stillbirth.

The diagnosis is usually made at operation, and suspected from scan or labour findings.

• Ultrasound at 34 to 38 weeks: lower segment thickness (below 2.3 mm is a concern, below 2.0 mm is a high risk), a niche or defect in the scar, bladder wall changes.
• In labour: scar tenderness, cardiotocography abnormalities, vaginal bleeding.
• Operative finding: thin translucent scar with intact serosa, or a defect bridged by membranes or peritoneum.
• Haemoglobin and group and cross-match.

The principle is to avoid labour when a thin scar is found, to deliver by caesarean section when dehiscence is suspected and to repair the scar.

• Supportive: admit when scar pain, bleeding or a thin scar is found; avoid oxytocin and prostaglandins; two cannulae; continuous cardiotocography in labour; group and cross-match 2 units; plan birth in a theatre capable facility.
• Pharmacological: cefazolin 2 g IV as a single dose before caesarean section; oxytocin 10 IU IM after birth, then 20 IU in 1 litre Ringer's lactate at 125 mL per hour for 4 hours; tranexamic acid 1 g IV over 10 minutes if bleeding exceeds 500 mL; paracetamol 1 g oral 6-hourly (maximum 4 g in 24 hours); enoxaparin 40 mg subcutaneous daily for 10 days after emergency caesarean section; ferrous sulphate 200 mg oral 8-hourly for 3 months if anaemic.
• Procedures: elective caesarean section at 36 to 37 weeks for a thin scar (below 2.0 mm) or a defect found in late pregnancy; emergency caesarean section for suspected dehiscence in labour; layered closure of the defect with a double layer repair, and hysterectomy only for uncontrolled bleeding.
• Special groups: dehiscence found at caesarean section means later births should be planned repeat caesarean sections at 36 to 37 weeks, with an interval of at least 18 months before conception.
• Red flags: constant scar pain, bleeding, fetal bradycardia, loss of contractions, shock, haematuria.
• Follow-up: wound and bladder review at 1 week; haemoglobin at 24 hours; review at 6 weeks; written record of the finding for later pregnancies.