Low vitamin B12 in pregnant women has an effect on the fetus and may lead to megaloblastic anemia in pregnant women, resulting in fetal malformations, preterm delivery, stillbirth and other serious effects. Vitamin B12 is the main ingredient needed by the body to synthesize red blood cells, if the body is deficient, it can lead to nutritional anemia. Anemia during pregnancy will cause certain damage to the development of pregnant women and the fetus, of which, severe anemia can cause intrauterine distress, preterm delivery, and in severe cases, even stillbirth. Vitamin B12, as a cobalt-containing porphyrin compound, cannot be synthesized by the body itself, and needs to be supplemented by external food. When the body is deficient in vitamin B12, it will lead to megaloblastic anemia and fetal malformations in pregnant women. Therefore, pregnant women should consume more meat, eggs, milk and other nutritious food during pregnancy. If the level of vitamin B12 is not normalized by strengthening the diet of pregnant women, they should go to the hospital in time and take vitamin B12 supplements under the guidance of the doctor.