Twins, DizygoticTwins, MonozygoticTwinsDiseases in TwinsTwins, ConjoinedTwin Studies as TopicPregnancy, TwinPregnancy, MultipleTripletsEnvironmentPregnancyTwinning, MonozygoticFetofetal TransfusionGenetics, BehavioralGene-Environment InteractionRegistriesInheritance PatternsDenmarkBirth WeightMaternal Serum Screening TestsInfant, NewbornHeredityChorionGenetic Predisposition to DiseaseQuantitative Trait, HeritableModels, Genetic