Fetal macrosomia as a risk factor for shoulder dystocia during vacuum extraction

Objective: Vacuum extraction of a macrosomic fetus is considered a risk factor for shoulder dystocia (SD). We evaluated maternal and fetal outcomes following vacuum extraction of macrosomic infants.Methods: A retrospective cohort study conducted in two large teaching hospitals. All deliveries of macrosomic infants by vacuum extraction and vaginal delivery were compared. The primary outcome measure was SD. Secondary outcome measures were severe perineal lacerations and postpartum hemorrhage. For statistical analysis, we used McNemar's test and (2) or Fisher's exact tests. Odds ratios were analyzed via a logistic regression model.Results: From 2003 to 2013, there were 6019 (5.45%) deliveries of macrosomic fetuses, and 230 (0.21%) were delivered by vacuum extraction. There were 23 (10%) and seven (3.04%) cases of SD in the study and control groups, respectively. The risk of SD was significantly higher in the study group (p>0.05). We found a significant association between SD and vacuum delivery [p=0.003; OR=3.54 (95% CI: 1.49-8.42)]. The composite adverse neonatal outcome rate was 6.5% (15/230) and 1.7% (4/230) in the study and control groups, respectively (p=0.009).Conclusion: Vacuum extraction of a macrosomic infant is a risk factor for shoulder dystocia but not for postpartum hemorrhage or severe vaginal tears.