AnencephalySpina Bifida OccultaSpinal DysraphismNeural Tube DefectsPregnancyBirth WeightInfant, NewbornCongenital AbnormalitiesEncephaloceleFetal DeathPregnancy, TwinFolic AcidDiseases in TwinsPremature BirthAmniotic Band SyndromePrenatal CareInfant, Low Birth WeightFetal DiseasesGestational AgeBirth RatePrenatal DiagnosisPreconception CareAmniotic FluidPregnancy OutcomeFood, Fortified