© 2015 by Thieme Medical Publishers, Inc. Objective The objective of this study was to examine the relationship between positive glucose challenge test (GCT) values and perinatal outcomes stratified by maternal body mass index (BMI). Study Design Retrospective cohort of singleton gestations with a GCT performed at >20 weeks and documented BMI at entry to care. Subjects were classified by GCT level and BMI. Primary outcomes included large for gestational age (LGA), macrosomia, shoulder dystocia, and pregnancy-induced hypertension. Cochran-Armitage tests for trend and logistic regression were used to compare the GCT categories. Results A total of 14,525 women met enrollment criteria-8,521 with a GCT < 120 mg/dL and 6,004 with a GCT ≥ 120 mg/dL. When BMI < 25 kg/m2 was considered, the risks were not increased at any level of GCT for any outcome. However, for subjects with BMI ≥ 25 kg/m2, the risk of LGA for a GCT 130 to 134 mg/dL was increased, but not at GCT of 135 to 139 mg/dL (p < 0.001). Similar, but nonsignificant, trends were observed for macrosomia and shoulder dystocia. Conclusion Increasing GCT is associated with adverse outcomes primarily in women with a BMI ≥ 25 kg/m2. Women with a BMI ≥ 25 kg/m2 and a GCT 135 to 140 mg/dL appear to have less risk of LGA than women with GCT 130 to 134 mg/dL, suggesting a possible effect of diagnosing and treating gestational diabetes mellitus in this group.