Correlation of increased fetal asymmetry with shoulder dystocia in the nondiabetic woman with suspected macrosomia

OBJECTIVE: To determine if the sonographic difference of ≥ 2.6 cm between the fetal abdominal diameter (AD) and biparietal diameter (BPD), a proxy for fetal asymmetry, has an association with shoulder dystocia in nondiabetic women with suspected macrosomia. STUDY DESIGN: A retrospective cohort study was performed in 3 Southern California tertiary care hospitals. We identified patients in whom sonographic evaluation after 36 weeks' gestation demonstrated an estimated fetal weight > 4,000 g. Additional prenatal and delivery information was obtained from hospital records. RESULTS: We identified 159 subjects who met ultrasound criteria and underwent a vaginal delivery. The mean AD-BPD difference in the shoulder dystocia group was significantly greater than in the group without shoulder dystocia (2.76 ± 0.59 vs. 2.37 ± 0.56, p = 0.001). The adjusted OR of shoulder dystocia in the group with an AD-BPD difference ≥ 2.6 was 3.67 (95% CI, 1.44-9.36). CONCLUSION: Significant discordance between the fetal head and abdomen appears to be associated with an increased rate of shoulder dystocia in a nondiabetic population with suspected macrosomia.