Currently, over one-third of reproductive-aged women in the U.S. are obese [body mass index (BMI) ≥ 30]. Our research team has shown that we can improve birth weight outcomes in babies of obese women who start a weight-management intervention program at 14 to 15 weeks of their pregnancy (soon after their first prenatal visit). However, organogenesis and metabolic programming begin early in the first trimester, well before the first prenatal visit. Therefore, waiting to address mothers' weight, physical activity, and diet quality until the first prenatal visit is not optimal. Given the need to reach overweight and obese women prior to pregnancy, and the Institute of Medicine's (IOM's) recent recommendation, based on observational studies, that women should reach a healthy weight before conceiving, this randomized clinical trial will evaluate a comprehensive preconception weight loss program.