Sonographic fetal asymmetry predicts shoulder dystocia

Abstract

Objective. The purpose of this study was to evaluate the performance of a sonographic measurement of fetal asymmetry, abdominal diameter minus biparietal diameter (AD - BPD), in the prediction of shoulder dystocia (SD) in a patient population that was unselected for diabetes mellitus (DM) status. Methods. Patients who underwent sonographic estimations of fetal biometric measurements within 14 days of vaginally delivered live-born singleton neonates weighing 3400 g or greater at a tertiary care institution were included in this retrospective cohort. The mean AD - BPD was retrospectively compared in deliveries complicated by SD with those without SD by the Student t test. A receiver operating characteristic curve was generated to determine the optimal cutoff for SD prediction. Test performance characteristics of AD - BPD were determined. Results. Of 5204 deliveries, 332 met inclusion criteria. Shoulder dystocia complicated 23 deliveries (6.9%). The mean AD - BPD was significantly higher in the dystocia group (2.39 versus 1.97; P = .0002). With an AD - BPD of 2.6 cm or greater, the risk rates of SD were 25% for unselected patients and 38.5% with DM. Conclusions. An AD - BPD of 2.6 cm or greater identifies a subset of patients with and without DM at risk for SD. © 2007 by the American Institute of Ultrasound in Medicine.