A woman with a previous classical cesarean section presents for planning of her third pregnancy. She is advised against a trial of labour. What is the estimated risk of uterine rupture with a classical (vertical body) uterine incision compared to a low transverse uterine incision, and why does this anatomical difference matter?

• A Classical incision: 4–9% rupture risk in subsequent pregnancy (can occur before labour onset); low transverse: 0.5–1% rupture risk occurring almost exclusively during active labour ✓
• B Classical incision: 1–2% risk; low transverse: 3–5% risk due to extension into lower segment during active labour
• C Both classical and low transverse carry equal rupture risk of 0.5–1% when elective repeat cesarean is performed at 37 weeks
• D Classical incision risk is 10–15% and affects uterine vascularity necessitating hysterectomy in all rupture cases

Explanation

The classical uterine incision (vertical, involving the upper uterine body) carries a 4–9% risk of rupture in subsequent pregnancies, and critically, this rupture can occur BEFORE labour onset (antepartum rupture) due to the poor healing characteristics of the thick, active fundal myometrium. Low transverse incisions have 0.5–0.9% rupture risk during labour only (rarely antepartum), because the lower uterine segment heals better and is less active. This distinction drives the recommendation for classical incision scars to have elective repeat cesarean at 36–37 weeks, before spontaneous labour begins — unlike low transverse where TOLAC (trial of labour after cesarean) may be offered.

Reference: Williams Obstetrics, 26th ed.

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Written and medically reviewed by the StethoPrep medical team.