Although ACOG recommends screening obese women early for gestational diabetes (GDM), no studies demonstrate an improvement in perinatal outcomes. We sought to determine if early GDM screening improves pregnancy outcomes in obese women. We performed a randomized controlled trial of obese women (BMI≥30 kg/m2) with non-anomalous, singleton gestations <20wks comparing early GDM screening (14-20 wks) to routine (24-28 wks). GDM screening was performed using a 50-g, 1-hr glucose challenge test followed by a 100-g, 3-hr glucose tolerance test if ≥135 mg/dL. GDM was diagnosed using Carpenter Coustan criteria. HbA1c was measured on all patients; the provider was notified and GDM diagnosed if ≥6.5%. Women not diagnosed at 14-20 wks were rescreened at 24-28 wks. Exclusion criteria were diabetes, major medical illness (cardiac, hemoglobinopathy, prednisone), bariatric surgery, and prior cesarean. The primary outcome was a composite of macrosomia (>4000g), primary cesarean, hypertensive disease of pregnancy (PIH), shoulder dystocia, neonatal hyperbilirubinemia, and neonatal hypoglycemia. We estimated a 50% incidence of the primary composite outcome; to detect a 50% reduction in the GDM patients (α=0.05, β=0.2), 58 GDM patients per group were necessary. The total sample size of 950 estimated a 14% incidence of GDM in obese women. This sample would also have 80% power to detect a 10% absolute change in the primary outcome for the entire population. Of 954 women enrolled, 912 (95.6%) had outcomes. Randomization groups were balanced at baseline for race, BMI, nulliparity, gestational age at randomization, and HbA1c. Of the 454 (49.7%) randomized to early screening, 69 (15.2%) were diagnosed with GDM: 29 (6.4%) <20 wks and 40 (8.8%) >24 wks. Of 458 randomized to routine screening, 56 (12.2%) had GDM. Early screening did not reduce the incidence of the primary outcome as it was nominally higher in the early group (59.0% vs 53.3%, p=0.08. PIH was not reduced in the early group (13.5% vs 9.6%, p=0.06). Use of insulin was significantly increased in the early group (2.6% vs 0.7%, p=0.02). These findings were consistent when only those with GDM were compared; considering only GDM, women in the early group were delivered earlier than the routine group. In this RCT, early GDM screening in obese women was not beneficial and may have been harmful. Recommendations for early GDM screening need to be reassessed in light of these findings.