Multiple Birth OffspringUterusPregnancy, MultipleTripletsBirth RatePregnancyQuadrupletsBirth WeightReproductive Techniques, AssistedMaternal AgeTwinsInfant, NewbornPremature BirthInfant, Low Birth WeightPregnancy OutcomeInfant MortalityBirth OrderFetal DeathGestational AgeCongenital AbnormalitiesFertilization in VitroBirth CertificatesPregnancy ComplicationsPrenatal Exposure Delayed EffectsInfertilityPerinatal CareDelivery, ObstetricPregnancy Reduction, MultifetalLive Birth