Folic acid is usually taken after pregnancy until the third trimester, due to the fact that it is a water-soluble vitamin. It has been shown to prevent neural tube abnormalities in the fetus. Some scientists have found that after taking folic acid during the high incidence of neural tube abnormalities, it can prevent 85% of them. The development of the fetal neural tube is usually completed in the first trimester of pregnancy, so in clinical practice, doctors usually take folic acid in the first and second trimesters of pregnancy at a dose of 0.4 mg. If you are already pregnant, you can take it until the third trimester. If you have the conditions, you can go to the hospital to have a blood test to check the concentration of folic acid in the blood, and if the concentration is low, you may need to take 0.8mg per day.