Recent Institute of Medicine recommendations for weight gain in pregnancy advocate a marked increase over prior guidelines, and for reasons that must be questioned. The objectives of these new guidelines are to reduce perinatal mortality, prematurity, and fetal growth retardation. Evidence of a causal relationship between less maternal weight gain and these adverse outcomes is lacking. In addition, the consequences of increased pregnancy weight gain have been incompletely assessed. The risk-to-benefit ratio may be prohibitive. The new recommendations, which will be considered by many to be clinical guidelines, fall short of the formulation criteria recommended by the United States Preventive Services Task Force.