UterusTwinsDiseases in TwinsPregnancyTwins, MonozygoticTwins, ConjoinedTwins, DizygoticPregnancy OutcomePregnancy ComplicationsPregnancy, AnimalPregnancy, TwinPregnancy, EctopicPregnancy, MultipleTwin Studies as TopicPregnancy Trimester, FirstPregnancy Trimester, ThirdPregnancy RatePregnancy Complications, CardiovascularPregnancy TrimestersPregnancy TestsPregnancy Trimester, SecondPregnancy, TubalPregnancy in DiabeticsEmbryo ImplantationPregnancy Complications, NeoplasticGestational AgePregnancy in AdolescencePregnancy Complications, InfectiousPregnancy ProteinsAbortion, SpontaneousPlacentaFetal DeathPregnancy, High-RiskInfant, NewbornPregnancy, UnplannedPregnancy, UnwantedProgesteroneMyometriumDeciduaEndometriumUterine ContractionEmbryo TransferUltrasonography, PrenatalPregnancy Complications, HematologicPre-EclampsiaCervix UteriPregnancy MaintenancePregnancy, ProlongedFertilization in VitroPregnancy Reduction, MultifetalBirth WeightEstradiolAbortion, InducedPregnancy, AbdominalLabor, ObstetricCesarean SectionUterine DiseasesUterine NeoplasmsMaternal-Fetal ExchangeParityTripletsPregnancy Complications, ParasiticFetofetal TransfusionPrenatal CarePseudopregnancyFetusMaternal AgeInfertility, FemalePrenatal Exposure Delayed EffectsFetal Growth RetardationEstrusCongenital AbnormalitiesPremature BirthTrophoblastsObstetric Labor, PrematureOvariectomyFallopian TubesFetal DevelopmentDelivery, ObstetricFertilityHypertension, Pregnancy-InducedRisk FactorsLactationInsemination, ArtificialReproductive Techniques, AssistedPrenatal DiagnosisEstrous CyclePlacentationChorionOvaryChorionic GonadotropinProspective StudiesSperm Injections, IntracytoplasmicFetal DiseasesPlacenta DiseasesAmniotic FluidParturitionAbortion, TherapeuticCohort StudiesAbnormalities, Drug-Induced