When there is a moderate risk of folic acid metabolism, it is necessary to increase the dose of oral folic acid, for example, 400ug of folic acid per day during the first 3-6 months of pregnancy, 800ug per day during early pregnancy, and 400ug per day during the middle and late pregnancy, that is, 13-40 weeks. Oral folic acid can prevent fetal neural tube abnormality, congenital heart disease, cleft lip and palate, Down’s syndrome, developmental delay and low birth weight, as well as placental abruption, spontaneous miscarriage, including premature birth, pre-eclampsia and postpartum depression.