TwinsDiseases in TwinsTwins, MonozygoticPregnancyTwins, ConjoinedTwins, DizygoticPregnancy OutcomePregnancy ComplicationsIncidencePregnancy, AnimalPregnancy, TwinPregnancy, EctopicPregnancy, MultipleTwin Studies as TopicPregnancy Trimester, FirstPregnancy Trimester, ThirdPregnancy RatePregnancy Complications, CardiovascularPregnancy TrimestersPregnancy TestsPregnancy Trimester, SecondPregnancy in DiabeticsPregnancy, TubalInfant, NewbornPregnancy Complications, NeoplasticGestational AgePregnancy in AdolescencePregnancy Complications, InfectiousAbortion, SpontaneousPregnancy, High-RiskPregnancy ProteinsFetal DeathPregnancy, UnplannedRisk FactorsPregnancy, UnwantedPregnancy Complications, HematologicUltrasonography, PrenatalPlacentaPre-EclampsiaProspective StudiesBirth WeightPregnancy, ProlongedRetrospective StudiesPregnancy Reduction, MultifetalCohort StudiesFertilization in VitroEmbryo TransferAbortion, InducedUterusPregnancy, AbdominalParityTripletsPregnancy Complications, ParasiticTime FactorsEmbryo ImplantationFetofetal TransfusionPrenatal CareMaternal AgeCesarean SectionPregnancy MaintenanceMaternal-Fetal ExchangePrenatal Exposure Delayed EffectsRegistriesFetal Growth RetardationCongenital AbnormalitiesPremature BirthObstetric Labor, PrematureFollow-Up StudiesDelivery, ObstetricHypertension, Pregnancy-InducedFetal DevelopmentFetusPrenatal DiagnosisInfertility, FemaleProgesteroneReproductive Techniques, AssistedLactationLabor, ObstetricPrevalenceSperm Injections, IntracytoplasmicFetal DiseasesInfant, Low Birth WeightChorionTreatment OutcomeAbortion, TherapeuticAbnormalities, Drug-InducedDeciduaDiabetes, GestationalFertilityChorionic GonadotropinDenmarkMaternal ExposureInsemination, ArtificialUnited StatesPuerperal DisordersAge DistributionAmniotic FluidPlacenta DiseasesSwedenTrophoblasts