Fetal period is characterized by the rapid growth and maturation of tissues and organs. There are various alterations in carbohydrate, lipid and protein metabolisms in mother to provide nutrition to fetus. If something is wrong about these metabolisms in mother, this will indirectly affect fetus. So it is essential to elucidate the maternal and fetal carbohydrate, lipid and protein metabolisms in the management of a pregnant woman. Mild fasting hypoglycemia, postprandial hyperglycemia, hyperinsulinemia and increased peripheral insulin resistance are the characteristics of pregnancy. The fetus primarily depends on glucose as the energy source but can also use other substrates such as lactate, keto acids, amino acids, fatty acids and glycogen as energy sources. Proteins are needed as structural components. Alterations in lipid metabolism cause accumulation of maternal fat stores in the early pregnancy in order to enhance lipolysis in the late pregnancy providing glucose and amino acids for fetus while promoting usage of lipids as maternal energy source. Maternal energy metabolism affects fetal energy metabolism both in short and long terms. By the clarification of maternal and fetal energy metabolisms, it may be possible to predict and prevent some diseases of a newborn in the future.