TwinsDiseases in TwinsTwins, MonozygoticTwins, ConjoinedTwins, DizygoticTwin Studies as TopicPregnancy, TwinPregnancy, MultipleFetofetal TransfusionPregnancyTripletsEnvironmentPregnancy Reduction, MultifetalGestational AgeInfant, NewbornChorionFetal DeathPregnancy OutcomeUltrasonography, PrenatalGenetics, BehavioralBirth WeightGene-Environment InteractionPhenotypeTwinning, MonozygoticRegistriesSocial EnvironmentFetoscopyReproducibility of ResultsModels, GeneticGenetic Predisposition to DiseaseRisk FactorsCohort StudiesMolecular Sequence DataQuadrupletsDenmarkPolyhydramniosTime FactorsSwedenDermatoglyphicsReproductive Techniques, AssistedAlgorithmsFertilization in VitroTwin StudyEmbryo TransferBirth OrderLongitudinal Studies