Impact of Third-Trimester Measurement of Low Uterine Segment Thickness and Estimated Fetal Weight on Perinatal Morbidity in Women With Prior Cesarean Delivery

Objectives: This study aimed to estimate the impact of third-trimester ultrasound with measurement of the lower uterine segment thickness (LUST) and estimation of fetal weight (EFW) on maternal and perinatal morbidity among women with a prior cesarean delivery. Methods: We performed a secondary analysis of the QUARISMA trial, including women who delivered at term after one prior cesarean delivery in tertiary care centres. Major and minor maternal and perinatal morbidities were compared between centres that had introduced LUST and EFW measurements into routine practice and those that had not, using generalised estimating equations and adjusted odds ratios (aOR). In a secondary analysis, we compared women who underwent a trial of labour with and without LUSTand EFW measurements. Results: We observed a significant reduction in major perinatal morbidity (aOR 0.52; 95% CI 0.28-0.96, P = 0.04), minor perinatal morbidity (aOR 0.49; 95% CI 0.25-0.96, P = 0.04), and minor maternal morbidity (aOR 0.56; 95% CI 0.34- 0.94, P = 0.03) but no significant difference in major maternal morbidity (aOR 0.40; 95% CI 0.04-3.69, P = 0.42) in the 2 centres that had introduced third-trimester ultrasound with EFW and LUST measurements (1458 women), compared with the 4 centres (1247 women) that had not. Among women who underwent a trial of labour, we observed a reduction in major perinatal morbidity (aOR 0.25; 95% CI 0.11-0.54, P < 0.001) and a lower rate of uterine rupture (0% vs. 0.3%, P = 0.045) with LUST and EFW measurements. Conclusion: Third-trimester ultrasound with EFW and LUST measurement is associated with a significant reduction in major perinatal morbidity in women with a prior cesarean delivery.