The size of the fetus is related to the diet of the pregnant woman. If the pregnant woman consumes too little diet, it may result in the fetus being too small in size. If the pregnant woman is overnourished, the fetus may be too large. The size of the fetus is closely related to the diet of the pregnant woman, as the main source of nutrients absorbed by the fetus is the mother. Therefore, if a pregnant woman has poor dietary habits, partiality, not eating staple food, or excessive dieting, it may lead to small size of the fetus, which may seriously lead to poor development of the fetus and affect the growth and development of the fetus. If pregnant women consume excessive high-fat, high-calorie and high-cholesterol food during pregnancy, it may lead to oversized fetus, resulting in macrosomia, which may cause obstructed labor. The diet of pregnant women should be reasonable and standardized, avoiding the intake of too little or too much food, and focusing on nutritious and easily digestible food. Pregnant women should follow the doctor’s instructions to have regular checkups so as to understand the growth and development of the fetus. If physically possible, appropriate light activities are conducive to the growth and development of the fetus.