During pregnancy, the mother adapts her metabolism to ensure the continuous supply of nutrients to the fetus in order to sustain its exponential growth. Of the nutrients that cross the placenta, glucose is quantitatively the most important, followed by amino acids. Although lipids cross the placenta in much lower quantities, maternal lipid metabolism is consistently and intensely affected during pregnancy in order to satisfy both maternal and fetal needs. Fetal growth and development also depend on other essential nutrients, like vitamins. The metabolism of certain vitamins is therefore affected during pregnancy to ensure their proper availability to the fetus. The purpose of this chapter is to review the main changes in carbohydrate, amino acid, lipid, and vitamin metabolisms that take place throughout pregnancy under normal conditions.