Objective: The objective of the study was to compare pregnancy outcomes by completed week of gestation after 39 weeks with outcomes at 39 weeks. Study Design: Secondary analysis of a multicenter trial of fetal pulse oximetry in spontaneously laboring or induced nulliparous women at a gestation of 36 weeks or longer. Maternal outcomes included a composite (treated uterine atony, blood transfusion, and peripartum infections) and cesarean delivery. Neonatal outcomes included a composite of death, neonatal respiratory and other morbidities, and neonatal intensive care unit admission. Results: Among the 4086 women studied, the risks of the composite maternal outcome (P value for trend <.001), cesarean delivery (P <.001), and composite neonatal outcome (P =.047) increased with increasing gestational age from 39 to 41 or more completed weeks. Adjusted odds ratios (95% confidence interval) for 40 and 41 or more weeks, respectively, compared with 39 weeks were 1.29 (1.03-1.64) and 2.05 (1.60-2.64) for composite maternal outcome, 1.28 (1.05-1.57) and 1.75 (1.41-2.16) for cesarean delivery, and 1.25 (0.86-1.83) and 1.37 (0.90-2.09) for composite neonatal outcome. Conclusion: Risks of maternal morbidity and cesarean delivery but not neonatal morbidity increased significantly beyond 39 weeks. © 2012 Mosby, Inc.