Oral folic acid tablets taken during the first 3 months of pregnancy and the second 3 months of pregnancy can effectively prevent neural tube abnormalities in the fetus. Because folic acid deficiency in pregnant women can lead to the accumulation of cysteine in the body, which is embryotoxic and can easily cause fetal neural tube malformation, such as hydrocephalus and spina bifida, oral folic acid can effectively prevent fetal neural tube malformation. After the middle of pregnancy, since the fetus has already developed and formed, no fetal neural tube malformation will occur, so pregnant women can stop taking folic acid orally. However, if pregnant women with impaired folic acid metabolism do not take additional folic acid supplements, it may lead to folic acid deficiency and anemia will occur, so these people can take folic acid orally until the whole pregnancy.