Regarding uterine rupture scar assessment in trial of labor after cesarean (TOLAC), the MOST important sonographic predictor of scar dehiscence risk is:
- A Cervical length < 25 mm at 36 weeks
- B Lower uterine segment (LUS) thickness < 2 mm on transvaginal ultrasound at 36–38 weeks ✓
- C Uterine artery resistance index > 0.8 at scar site
- D Posterior placenta implanted over the cesarean scar
Explanation
Lower uterine segment (LUS) thickness measured by transvaginal ultrasound at 36–38 weeks is the most studied predictor of uterine scar integrity. A full-thickness LUS of < 2.0–2.3 mm is associated with significantly increased risk of uterine scar defect (niche) or rupture during TOLAC. A systematic review (Jastrow et al., 2010; Kok et al.) confirmed a cut-off of ≤ 2 mm correlates with scar dehiscence. A niche (uterine cesarean scar defect) > 50% of the adjacent myometrial thickness on saline infusion sonohysterography also predicts increased rupture risk. LUS measurement should be part of pre-TOLAC counseling.
Reference: Williams Obstetrics, 26th ed.
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Written and medically reviewed by the StethoPrep medical team.