Maternal malnutrition, ranging from under nutrition to over dietary intake before and in the pregnant state, is worldwide problem with significant consequences, not only for survival and increased risk for acute and chronic diseases both in mother and child, but also for economic productivity of individuals in the societies and additional costs on health system. Inter alia, pre-pregnancy underweight and insufficient gestational weight gain are considered as individual risk factors for the occurrence of spontaneous interruption, preterm birth, fetal growth restriction, and hypertensive disorders, strongly associated with poorer perinatal outcome. In a portion of this population, major eating disorders (anorexia and bulimia nervosa), once thought to be rare, but nowadays enlarged due to cultural pressure on the drive for thinness, have been identified as the etiology of an abnormal nutritional condition in developed countries, in contrast to long standing food deprivation in developing countries. Actually, even if without a complete weight management guidance for these selected pregnant women, an appropriate weight gain is recommended during pregnancy. Mainly, therapeutic approach is prevention using specific programs of improving weight before pregnant status. In this article, a review of the literature on selected obstetrical risks associated with maternal underweight has been performed and both the target prevention and management strategies have been described.