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Antenatal Prediction of Shoulder Dystocia and Birth Trauma Using Routine Maternal and Ultrasound Variables:
Anat Schwartz1, Monica Minopoli1, Chiara Di Ilio2
1Fetal Medicine Unit, St. George's University Hospitals NHS Foundation Trust, London, UK.
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.
