A woman requests elective repeat cesarean section (ERCS) at 39 weeks. She is counseled about Trial of Labor After Cesarean (TOLAC). Which factor in her history represents the STRONGEST absolute contraindication to TOLAC?

• A Previous classical (vertical) uterine incision ✓
• B Previous single lower segment cesarean section with residual scar thickness <2.3 mm on ultrasound
• C BMI of 40 kg/m² with current pregnancy estimated at 4.2 kg
• D Interpregnancy interval of 15 months since the previous cesarean section

Explanation

A previous classical (vertical, corporal) uterine incision is an absolute contraindication to TOLAC. Classical incisions carry a uterine rupture risk of 4–9% during labor (vs 0.5–1% for lower transverse scar), due to the incision traversing the contractile upper uterine segment. Rupture of a classical scar occurs in active labor and can be catastrophic. Lower segment scar thickness <2.3 mm (B) on ultrasound is a relative caution — while lower thickness may indicate a thinner scar, it is not an absolute contraindication; the evidence correlating specific thickness to rupture risk is not strong enough to make it an absolute contraindication in current guidelines. BMI 40 (C) and short interpregnancy interval (D) are relative risk factors that modify counseling but are not absolute contraindications.

Reference: Williams Obstetrics, 26th ed.

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Written and medically reviewed by the StethoPrep medical team.