Multiple Birth OffspringPregnancy, MultipleTripletsBirth RatePregnancyQuadrupletsBirth WeightReproductive Techniques, AssistedMaternal AgeTwinsInfant, NewbornPremature BirthInfant, Low Birth WeightPregnancy OutcomeInfant MortalityBirth OrderFetal DeathEmbryo TransferGestational AgeCongenital AbnormalitiesFertilization in VitroBirth CertificatesPrenatal Exposure Delayed EffectsPregnancy ComplicationsInfertilityPerinatal CareRisk FactorsDelivery, ObstetricPregnancy Reduction, MultifetalLive Birth