The main goal of this study is to examine the comparative effectiveness of diabetes prevention strategies in women with Gestational Diabetes Mellitus (GDM) on the control of the following conditions: obesity, hyperglycemia, hypertension and depression. This randomized lifestyle intervention study will be conducted at Kaiser Permanente Northern California. Women in the intervention will receive a letter on gestational weight gain during pregnancy and in the postpartum period, a curriculum of individualized lifestyle counseling via telephone, augmented with e-mail and an interactive Web site. Patients randomized to the usual care arm will receive the standard-care telephone calls from the Perinatal Center during pregnancy and the Center's printed educational materials postpartum. Outcomes will be assessed through the electronic medical record and patient surveys conducted during pregnancy and at 6-weeks, 6- months and 1-year postpartum.