The development of fetal bones and teeth requires a large amount of calcium from the body of pregnant women. To avoid osteoporosis caused by calcium loss and to meet the nutritional needs of the fetus, pregnant women are often clinically required to take calcium supplements. It is generally recommended to start calcium supplementation after the third month of pregnancy, with 1-2g of calcium daily, which can prevent hypertensive diseases during pregnancy as well as prevent gastrocnemius muscle spasm caused by calcium deficiency in pregnant women. Under normal circumstances, the appropriate intake of calcium for pregnant women in early pregnancy is 800mg/d. Through a reasonable diet, sufficient calcium can be obtained and no additional calcium supplementation is needed. If a pregnant woman’s diet cannot meet the 800 mg intake in early pregnancy, she needs to consume calcium-containing foods or calcium supplements. In the middle of pregnancy (4-6 months), the calcium intake of pregnant women is 1000mg/d. At this time, the fetal teeth and bones have started to develop, and the need of pregnant women for calcium increases; in the late pregnancy (7-9 months), the need for calcium reaches 1200-1500mg/d. At this time, it is the final period of fetal teeth and bones calcification, and the diet may not meet the needs of fetal growth, so it is necessary to take calcium supplements from the middle of pregnancy. Therefore, it is necessary to take calcium from calcium-containing foods or high-quality calcium supplements from the middle of pregnancy. As mentioned above, for pregnant women, proper calcium supplementation is the key to ensure fetal development. It should be noted that oxalic acid and phytic acid may interfere with the absorption of calcium, so the best time to take calcium supplements is before bedtime or between meals.