Antenatal Prediction of Shoulder Dystocia and Birth Trauma Using Routine Maternal and Ultrasound Variables: Retrospective Cohort Study

Objective: To develop antenatal prediction models for shoulder dystocia and birth trauma using routinely collected maternal and sonographic variables. Design: Retrospective cohort study. Setting: Single tertiary referral centre in the UK. Population or Sample: All singleton term liveborn pregnancies delivered between January 2016 and November 2024 with a third-trimester ultrasound performed at or beyond 36 weeks' gestation. Methods: Multivariable logistic regression was used to develop antenatal prediction models for shoulder dystocia and birth trauma, incorporating maternal characteristics and fetal biometry including abdominal circumference (AC; centile or mm) and estimated fetal weight (EFW; grams or centile). Model performance was assessed using tests for multicollinearity, discrimination (area under the ROC curve, AUC) and calibration. Main Outcome Measures: Shoulder dystocia and birth trauma, the latter defined as a composite of shoulder dystocia, postpartum haemorrhage requiring blood transfusion, caesarean delivery at full dilatation, or hypoxic–ischaemic encephalopathy (HIE ≥ 1). Results: A total of 24 334 singleton term pregnancies were included; 432 (1.8%) were complicated by shoulder dystocia and 1210 (5.0%) by birth trauma. The model including maternal characteristics and AC centile demonstrated the best discrimination. For shoulder dystocia, the apparent AUC was 0.706 (95% CI 0.682–0.730); the optimism-corrected AUC after bootstrap validation was 0.699. For birth trauma, the apparent AUC was 0.669 (95% CI 0.654–0.685); the optimism-corrected AUC was 0.665. At a 10% false-positive rate, sensitivity was 31.5% for shoulder dystocia and 22.8% for birth trauma, compared with 20.4% and 14.0%, respectively, using EFW ≥ 90th centile. Conclusions: Antenatal models combining fetal AC centile with maternal risk factors outperform EFW-based thresholds currently used in clinical practice. Although discrimination was modest, the model may be useful for antenatal risk stratification and counselling, rather than as a stand-alone clinical test. Such models may help identify pregnancies at increased risk of delivery-related complications associated with fetal overgrowth and inform future studies evaluating targeted interventions.