We compared obstetric outcomes based on gestational weight gain in normal-weight and obese women using traditional Institute of Medicine (IOM) guidelines and newly recommended Cedergren criteria. Using the New Jersey Pregnancy Risk Assessment Monitoring System (PRAMS) database and electronic birth records, perinatal outcomes were analyzed to estimate the independent effects of prepregnancy body mass index (BMI) and gestational weight gain by IOM versus Cedergren criteria. Of 9125 subjects in PRAMS database from 2002 to 2006, 53.7% had normal BMI, 12.3% were overweight, 18.2% were obese, and the rest were underweight. Among normal-weight mothers, when compared with the IOM guidelines, macrosomia (6.45% versus 4.27%) and cesarean delivery rates (30.42% versus 29.83%) were lower using Cedergren criteria but the rates of preterm delivery (5.06% versus 9.44%), low birth weight (0.38% versus 2.42%), and neonatal intensive care unit (NICU) admissions (7.02% versus 10.86%) were higher with the Cedergren criteria. Similarly, among obese patients, when compared with IOM guidelines, macrosomia (10.79% versus 5.47%) and cesarean delivery rates (43.95% versus 40.71%) were lower using Cedergren criteria but the rates of preterm delivery (6.83% versus 8.32%), low birth weight (0.87% versus 1.88%), and NICU admissions (8.92% versus 13.78%) were higher with the Cedergren criteria. Based on our results, ideal gestational weight gain is presumably somewhere between the IOM and Cedergren's guidelines.