TwinsDiseases in TwinsTwins, MonozygoticTwins, ConjoinedTwins, DizygoticTwin Studies as TopicPregnancy, TwinPregnancy, MultipleFetofetal TransfusionPregnancyTripletsPregnancy Reduction, MultifetalEnvironmentGestational AgeFetal DeathChorionPregnancy OutcomeInfant, NewbornGenetics, BehavioralUltrasonography, PrenatalBirth WeightGene-Environment InteractionTwinning, MonozygoticSocial EnvironmentRegistriesFetoscopyQuadrupletsPolyhydramniosDenmarkDermatoglyphicsGenetic Predisposition to DiseaseReproductive Techniques, AssistedPhenotypeTwin StudySwedenBirth Order