Folic AcidFolic Acid DeficiencyNeural Tube DefectsTetrahydrofolatesDietary SupplementsHomocysteineFood, FortifiedVitamin B 12Vitamin B ComplexFolic Acid AntagonistsPreconception CareFolate Receptors, GPI-AnchoredHyperhomocysteinemiaAnemia, MacrocyticHematinicsVitamin B 6Pteroylpolyglutamic AcidsPregnancyVitamin B 12 DeficiencyFolic Acid TransportersDouble-Blind MethodBreadVitaminsPrenatal Care