Association of Fetal Abdominal–Head Circumference Size Difference With Shoulder Dystocia: A Multicenter Study

circumference ► head circumference ► shoulder dystocia Abstract Objective This study aims to determine if shoulder dystocia is associated with a difference in the fetal abdominal (AC) to head circumference (HC) of 50 mm or more noted on antenatal ultrasound. Study Design A multicenter matched case–control study was performed comparing women who had shoulder dystocia to controls who did not. Women with vaginal births of live born nonanomalous singletons 36 weeks of gestation with an antenatal ultrasound within 4 weeks of delivery were included. Controls were matched for gestational age, route of delivery, and diabetes status. Results We identified 181 matched pairs. Only 5 % of the fetuses had an AC to HC of 50 mm. The proportion of AC to HC difference of 50 mm was significantly higher in shoulder dystocia cases (8%) than controls (1%, p 0.002). With multivariate regression, the three significant factors associatedwith shoulder dystocia were AC toHC 50 mm (odd