Diet therapy for women pregnant with multiples is an important component of effective prenatal care. This chapter summarizes current research on maternal pregravid weight, gestational weight gain, carbohydrate metabolism, iron status, and vitamin and mineral intake on fetal growth and length of gestation in singletons and, when known, in twin and triplet gestations. Serum ferritin levels, which are lowered with iron deficiency and elevated in the presence of infection, have also been linked to prematurity. Prenatal use of vitamin-mineral supplements among low-income women has been shown to reduce the risks of preterm delivery and low birth weight, particularly if initiated during the first trimester. Infants whose mothers had higher omega-3 fatty acid levels at birth demonstrated better cognitive development. The pattern of maternal weight gain has been shown to be as important as total weight gain in its effect on birth weight in both singleton and twin pregnancies.