RESUMEN
OBJECTIVES: To study risk factors for shoulder dystocia (ShD) among women delivering <3500 g newborn. METHODS: A retrospective case-control study of all term live-singleton deliveries during 2011-2019. Women with neonatal birthweight <3500 g were included. We compared cases of ShD to other deliveries by univariate and multivariable regression. RESULTS: There were 79/41 092 (0.19%) cases of ShD among neonates <3500 g. In multivariable regression analysis, the following factors were independently associated with ShD; operative vaginal delivery (odds ratio [OR] 2.78; 95% confidence interval [CI]: 1.28-6.02, P = 0.009), vaginal birth after cesarean (VBAC, OR 2.74; 1.22-6.13, P = 0.010), sonographic abdominal circumference to biparietal diameter ratio (3.73 among ShD vs. 3.62, OR 1.35; 95% CI: 1.12-1.63, P = 0.001) and sonographic abdominal circumference to head circumference ratio (1.036 among ShD vs. 1.011, OR 3.04; 95% CI: 1.006-9.23, P = 0.049). CONCLUSIONS: There is an association between operative vaginal delivery and ShD also in deliveries <3500 g. Importantly, the proportions between the fetal head and abdominal circumference are a better predictor of ShD than the newborn fetal weight and VBAC is associated with ShD.