Prediction of preterm birth using <scp>3D</scp> volume cesarean scar morphology in pregnant women with previous advanced labor cesarean delivery

INTRODUCTION: This study aimed to develop a multiparameter predictive model for spontaneous preterm birth in pregnant women with a history of advanced labor cesarean delivery, using cesarean scar ultrasound characteristics. MATERIAL AND METHODS: This prospective observational cohort study included pregnant women with a history of advanced labor cesarean delivery (≥8 cm cervical dilatation) at University College London Hospitals (August 2019-August 2023). Participants underwent transvaginal ultrasound using validated protocols for cesarean scar evaluation. Measurements included scar distance to the internal os, niche dimensions (length, depth, and width), residual and adjacent myometrial thickness, and 3D niche and cervical volumes. Predictive models for spontaneous preterm birth and short cervical length ≤25 mm were developed using multivariable logistic regression, adjusting for potential confounders. RESULTS: During the surveillance period, 12.6% (21/166) of women developed a short cervix, and 23.5% (39/166) received preterm birth prophylactic interventions. Spontaneous preterm birth rate was 7.8% (13/166) <37 weeks and 4.8% (8/166) <34 weeks. The cesarean scar was visualized in 89.8% (149/166), with a niche identified in 48.3% (72/149) of women. Scars positioned at or caudal to the internal cervical os were associated with significantly higher risks of short cervix and/or spontaneous preterm birth compared to scars cranial to the internal os (aOR 5.26, 95% CI 1.59, 17.32, p = 0.006; aOR 5.00, 95% CI 1.10, 22.78, p = 0.037, respectively). Traditional predictive models based on cervical length and obstetric history demonstrated modest performance. Scar distance to the internal os consistently emerged as the strongest independent predictor of short cervix across all models (p < 0.001-0.005). Models incorporating 3D ultrasound scar parameters improved predictive accuracy, with the final model achieving AUC 0.91 (95% CI 0.81, 0.98) and 91% (95% CI 0.73, 1.00) sensitivity at FPR of 25% for spontaneous preterm birth. For short cervix prediction, the AUC was 0.89 (95% CI 0.80, 0.96), at 88% (95% CI 0.62, 1.00) sensitivity for the same FPR. CONCLUSIONS: 3D transvaginal ultrasound assessment of cesarean scar morphology was associated with improved prediction of spontaneous preterm birth in pregnant women with a history of advanced labor cesarean delivery; however, scar position relative to the internal os remained the strongest individual predictor.