Obesity, the most common metabolic disorder, concerns, among others, women of reproductive age and, when it occurs before or during pregnancy, constitutes a major risk factor for both maternal and fetal complications. The complications of obesity in a prospective mother include subfertility, miscarriage, thrombo-embolism, hypertensive disorders, metabolic syndrome, preterm delivery and higher frequency of cesarean section. Fetal complications include intrauterine death, congenital anomalies and macrosomia. Moreover, the complications of maternal obesity do not only involve the fetus; they also extend beyond fetal life into childhood and adulthood. The mother's diet during pregnancy creates a metabolic environment that affects fetal growth and may result in later development of metabolic syndrome and cardiovascular disease, a phenomenon known as "developmental origin of adult disease". Since the expectant mother is usually more motivated to accept lifestyle modifications, pregnancy is a period during which obesity can be more effectively managed. The control of body weight during this period is of paramount importance for pregnancy outcome as well as the health status of the mother and the neonate.