You can start to pay attention to calcium and iron supplementation around the 4th month of pregnancy to ensure the normal development of the fetus. At the beginning of the 4th month of pregnancy, the fetus’ bones and muscles grow and develop rapidly, and the demand for calcium is high. During this period, pregnant women who are deficient in calcium can easily develop symptoms of calcium deficiency, such as leg cramps, joint pain and poor resistance. Therefore, pregnant women in the middle and late stages of pregnancy can eat calcium-rich foods, such as dairy products and shrimp, and try to go outdoors to promote the synthesis of vitamin D and increase the absorption of calcium through the sun. As the fetus grows and develops, the blood volume increases, and the pregnant woman’s demand for iron becomes more and more in the fourth month of pregnancy. Therefore, the diet can be appropriately increased by eating more iron-rich foods, such as red meat, liver and egg yolk, etc. If the iron content from food is not enough to meet the physiological needs of pregnant women and fetuses, iron supplements are needed under the guidance of doctors. Therefore, the daily requirement of trace elements can be supplemented through a reasonable diet during pregnancy. If the requirement of the organism cannot be met, iron and calcium preparations can be used under the guidance of professional doctors as appropriate to avoid affecting the fetal development.