Twins, DizygoticTwins, MonozygoticDiseases in TwinsTwinsSiblingsTwins, ConjoinedTwin Studies as TopicSibling RelationsPregnancy, TwinEnvironmentTripletsPregnancy, MultipleTwinning, MonozygoticPregnancyRegistriesGene-Environment InteractionGenetics, BehavioralInheritance PatternsGenetic Predisposition to DiseaseDenmarkMaternal Serum Screening TestsPhenotypeFetofetal TransfusionHeredityQuantitative Trait, HeritableInfant, NewbornModels, GeneticBirth WeightSwedenSocial EnvironmentNuclear FamilyChimerismChorionRisk FactorsCohort StudiesPedigreeFinlandGenetic VariationSex FactorsMaternal AgeGenetic LinkageGenotypeGestational Age