Likelihood of vaginal delivery in pregnancies complicated by macrosomia

OBJECTIVE: To determine the labor characteristics, and likelihood of vaginal delivery in pregnancies complicated by macrosomia. STUDY DESIGN: Consecutive, nondiabetic pregnancies resulting in the delivery of a macrosomic fetus (≥4000 g) were compared to consecutive term non-macrosomic deliveries. Labor characteristics, labor abnormalities and mode of delivery were compared overall, and stratified by type of labor. RESULTS: Cesarean Section Rates (p < 0.05 vs control) No oxylocin Augmented Induced Overall Macro 3.6% (4/110) 23.4% (26/111) 44% (26/59) 20% (56/280) Control 1.7% (19/1137) 12.4% (93/749) 16.2% (58/359) 7.6% (170/2245) Overall, labor abnormalities were more frequent in Macrosomic than Control [15.9% vs 4.7%, O.K. 3.9 (2.6-5.7)]. In the subset of women undergoing induction of labor, the Macrosomic group had higher rates of both arrest of dilation (25.4% vs 6.4%, O.R. 4.7 (2.1-10.3)1 and arrest of descent [8.5% vs 1.1%, O.R. 8.2 (1.8-38)] than the Controls. The Macrosomic cases requiring augmentation also had a higher rate of arrest of descent than Controls [9% vs 2.4%, O.R. 4.98 (2.3-10.9)]. CONCLUSION: Spontaneous labor results in vaginal delivery in the vast majority of macrosomic pregnancies even if augmentation is required. Labor induction, however, has an extremely high risk of failure in the face of macrosomia. Any oxytocin requirement is associated with a greater increase in cesarean section rate for macrosomic than for non-macrosomic pregnancies.