Obesity is regarded as one of the major contemporary nutritional issues with features of a modern epidemic that affects not only the developed countries, but also the developing ones. Obesity can cause problems during pregnancy, concerning not only the maternal health and the outcome of pregnancy, but the subsequent health of the infant and the newborn as well. Obese pregnant women belong to the high-risk pregnancy group, as gestational diabetes mellitus, pre-eclampsia, and less frequently, infections and thromboembolic events can directly affect maternal health. The maternal and perinatal risks, associated with obesity in pregnancy, make it imperative today to treat this condition before and during pregnancy. The best and most effective treatment of obesity in pregnancy is prevention. Active weight loss interventions in obese pregnant women are prohibitive. Healthy diet and regular physical activity of pregnant women, are crucial steps towards the normal progression of the pregnancy. This article, based on the systematic citation of modern bibliographic data, attempts a brief review of the effects of the maternal obesity on the outcome of pregnancy and the role of nutrition and physical activity in the treatment of overweight and obese women, with the aim of ensuring the best in mother’s health and the perinatal outcome.