Twins, DizygoticTwins, MonozygoticDiseases in TwinsTwinsTwin Studies as TopicEnvironmentTripletsTwinning, MonozygoticPregnancy, MultipleMaternal Serum Screening TestsInheritance PatternsRegistriesGene-Environment InteractionGenetics, BehavioralPregnancy, TwinPregnancyDenmarkQuantitative Trait, HeritableHeredityChimerismModels, GeneticGenetic Predisposition to DiseaseBirth WeightPhenotypeSwedenInfant, NewbornChorionSiblingsSocial Environment