Objective: We sought to investigate the relationship between prepregnancy weight, treatment modality (diet or insulin), level of glycemic control, and pregnancy outcome. Study design: We recruited women with gestational diabetes (GDM) from inner city prenatal clinics. All women were instructed in the use of an intensified management protocol using memory reflectance meters. Outcomes were analyzed according to maternal prepregnancy body mass index (BMI, kg/m 2) categories: normal weight (BMI 18.5- 24.9), overweight (BMI 25- 29.9), and obese (BMI ≥ 30), and by diet or insulin therapy and glycemic control (mean blood glucose < 100 mg/dL = good control). Pregnancy outcome variables included a composite outcome (at least 1 of the following: neonatal metabolic complications, large- for- gestational age or macrosomic infants, NICU admission for >24 hours, and the need for respiratory support) (not including oxygen therapy). In addition to composite outcome, a bivariate analysis was performed for each single variable, including preeclampsia and cesarean section delivery. Results: Four thousand and one women were enrolled. Obese women who achieved targeted levels of glycemic control had comparable pregnancy outcomes to normal weight and overweight women only when they were treated with insulin. Normal weight women treated with diet therapy who achieved targeted levels of glycemic control had good outcomes, but obese women treated with diet therapy who achieved targeted levels of glycemic control, nevertheless, had a 2- to 3- fold higher risk for adverse pregnancy outcome when compared with overweight and normal weight patients with well- controlled GDM. Women with GDM who failed to achieve established levels of glycemic control had significantly higher adverse pregnancy outcomes in all 3 maternal weight groups. Conclusion: In obese women with BMI ≥ 30 with GDM, achievement of targeted levels of glycemic control was associated with enhanced outcome only in women treated with insulin. Objective: We sought to investigate the relationship between prepregnancy weight, treatment modality (diet or insulin), level of glycemic control, and pregnancy outcome. Study design: We recruited women with gestational diabetes (GDM) from inner city prenatal clinics. All women were instructed in the use of an intensified management protocol using memory reflectance meters. overcomes (BMI 25-29.9) , and obese (BMI ≥ 30), and by diet or insulin therapy and glycemic control (mean blood glucose <100 mg / dL = good control). Pregnancy outcome variables included a composite outcome (at least 1 of the following: neonatal metabolic complications , large- for-gestational age or macrosomic infants, NICU admission for> 24 hours, and the need for respiratory support (not including oxygen therapy). In addition to composite outcome, a bivariate analysis was performe d for each single variable, including preeclampsia and cesarean section delivery. Results: Four thousand and one women were enrolled. Obese women who achieved targeted levels of glycemic control had comparable pregnancy outcomes to normal weight and overweight women only when they were treated with insulin. Normal weight women treated with diet therapy who achieved targeted levels of glycemic control had good outcomes, but obese women treated with diet therapy who achieved targeted levels of glycemic control, nevertheless, had a 2- to 3-fold higher risk for adverse pregnancy outcome when compared with overweight and normal weight patients with well-controlled GDM. Women with GDM who failed to achieve established levels of glycemic control had significantly higher higher adverse pregnancy outcomes in all 3 maternal weight groups. Conclusion: In obese women with BMI ≥ 30 with GDM, achievement of targeted levels of glycemic control was associated with enhanced outcome only in women treated w ithinsulin.