TwinsDiseases in TwinsTwins, MonozygoticTwins, ConjoinedTwins, DizygoticTwin Studies as TopicPregnancy, TwinPregnancy, MultipleFetofetal TransfusionPregnancyTripletsEnvironmentPregnancy Reduction, MultifetalGestational AgeInfant, NewbornFetal DeathPregnancy OutcomeChorionUltrasonography, PrenatalGenetics, BehavioralBirth WeightGene-Environment InteractionTwinning, MonozygoticRegistriesSocial EnvironmentFetoscopyPhenotypeRetrospective StudiesGenetic Predisposition to DiseaseRisk FactorsQuadrupletsPolyhydramniosDenmarkDermatoglyphicsReproductive Techniques, AssistedCohort StudiesModels, GeneticSwedenMolecular Sequence DataFertilization in VitroTime FactorsTwin StudyBirth OrderEmbryo Transfer