Perinatal outcome of fetuses with a birth weight greater than 4500 g: an analysis of 3356 cases.

Objective: To assess the perinatal outcome in a series of macrosomic fetuses according to the intended mode of delivery, and to estimate the individual risk of shoulder dystocia and brachial plexus injury upon information available either prior the onset of labor or at delivery.

Study Design: Perinatal and postnatal information of 3356 women who delivered during a 10-year period a macrosomic fetus (>4500 g) in vertex presentation were analyzed. After the exclusion of cases with extraneous factors that may have affected the health of the neonate, patient and neonatal characteristics were compared according to the intended mode of delivery. The contribution of factors known prior labor and at the time of deliver on the occurrence of shoulder dystocia and brachial plexus injury was analyzed using multiple logistic regression analysis.

Results: During the study period, 2371 women were admitted to spontaneous labor, 778 underwent an induction of labor, and 207 had an elective cesarean section. All cases of shoulder dystocia (n=310), and brachial plexus injury (n=94) occurred among women who delivered vaginally. The rate of brachial plexus injury was higher in cases who had shoulder dystocia than in those who did not (58/310 versus 36/2329, P<0.001). The incidence of brachial plexus injury increases steadily from 0.8 in fetuses weighing 4500-4599 g to 2.86% in those weighing more than 5000 g (P<0.01) and from 2.1 in women taller than 180 cm to 12.5% in those shorter than 155 cm (P<0.05). After adjustment for confounding variables shoulder dystocia (OR 9.2, 95% C.I. 5.38; 15.59), operative vaginal delivery (OR 1.96, 95% C.I. 1.10; 3.49) and clavicular fracture (OR 2.9, 95% C.I. 1.31; 6.44) remained predictors of brachial plexus injury.

Conclusion: Since some of these risk factors are known prior to delivery, each woman whose fetus is suspected to weight more than 4500 g should be counseled on her individual risk of severe perinatal morbidity before a decision on the mode of delivery is taken.