AnencephalyFolic AcidNeural Tube DefectsFood, FortifiedNeural TubeSpinal DysraphismSpina Bifida OccultaFolic Acid DeficiencyFlourVitamin B ComplexDietary SupplementsBreadPregnancyPreconception CareVitamin B 12HomocysteineTetrahydrofolatesPrenatal CareCongenital AbnormalitiesNeurulationVitamin B 12 DeficiencyCerealsInfant, NewbornFetal DeathNutrition PolicyFolic Acid AntagonistsAnemia, Iron-DeficiencyIron, DietaryMicronutrientsCondimentsPregnancy, TwinNeural CrestHyperhomocysteinemiaAnemia, MacrocyticDiseases in TwinsVitamin B 6Folate Receptors, GPI-AnchoredNutritional RequirementsNutritional StatusPrenatal DiagnosisAmniotic Band SyndromeChick EmbryoNervous SystemVitaminsBiological AvailabilityNotochordHematinicsAmniotic FluidFetal DiseasesIronDietMethylenetetrahydrofolate Reductase (NADPH2)PrevalencePollen TubePrenatal Nutritional Physiological PhenomenaGene Expression Regulation, DevelopmentalGestational AgeUnited StatesPteroylpolyglutamic AcidsPregnancy Outcome